Revert "chromiumos-sdk & informational config: switch to main branch"

This reverts commit 2f14a5e90628e6e504c63b934c35f2e83959fcb5.

Reason for revert: breaks running on branches.  crbug.com/1168324

Original change's description:
> chromiumos-sdk & informational config: switch to main branch
>
> These external branch builders needs to track main. Added a todo to
> examine this config in the future for simplicity.
>
> BUG=chromium:1159924
> TEST=./regenerate_configs.sh
>
> Change-Id: I24d4c8eb594b0d901b88ac2c9c7c159544a1cc5a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2597939
> Commit-Queue: George Engelbrecht <engeg@google.com>
> Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
> Tested-by: George Engelbrecht <engeg@google.com>
> Auto-Submit: George Engelbrecht <engeg@google.com>
> Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2601153
> Reviewed-by: Mike Frysinger <vapier@chromium.org>
> Commit-Queue: Mike Frysinger <vapier@chromium.org>

Bug: chromium:1159924
Change-Id: Ic2fa7484b56aa56f6caeddd61d540f9696610087
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2691447
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: LaMont Jones <lamontjones@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: LaMont Jones <lamontjones@chromium.org>
Auto-Submit: LaMont Jones <lamontjones@chromium.org>
diff --git a/config/chromeos_config.py b/config/chromeos_config.py
index 277a2db..7534ca5 100644
--- a/config/chromeos_config.py
+++ b/config/chromeos_config.py
@@ -209,7 +209,6 @@
       'informational',
       display_label=config_lib.DISPLAY_LABEL_INFORMATIONAL,
       description='Informational Builds',
-      manifest_branch='main',
       luci_builder=config_lib.LUCI_BUILDER_INFORMATIONAL,
   )
 
@@ -2868,11 +2867,6 @@
       site_config.templates.no_hwtest_builder,
       # The amd64-host has to be last as that is when the toolchains
       # are bundled up for inclusion in the sdk.
-      #
-      # TODO(crbug.com/1159924): Audit this and other builder's branch
-      # since we deprecated the old external tracking branch.
-      manifest_branch='main',
-
       boards=[
           'arm-generic', 'amd64-generic'
       ],
diff --git a/config/config_dump.json b/config/config_dump.json
index 5d7a89e..aefe85b 100644
--- a/config/config_dump.json
+++ b/config/config_dump.json
@@ -347,7 +347,6 @@
             "image_test": true,
             "images": [],
             "luci_builder": "Informational",
-            "manifest_branch": "main",
             "packages": [
                 "virtual/target-fuzzers"
             ],
@@ -378,8 +377,7 @@
             "_template": "informational",
             "description": "Informational Builds",
             "display_label": "informational",
-            "luci_builder": "Informational",
-            "manifest_branch": "main"
+            "luci_builder": "Informational"
         },
         "llvm_next_toolchain": {
             "_template": "llvm_next_toolchain",
@@ -1050,7 +1048,6 @@
         "doc": "https://dev.chromium.org/chromium-os/build/builder-overview#TOC-Continuous",
         "hw_tests_override": [],
         "luci_builder": "Informational",
-        "manifest_branch": "main",
         "schedule": "0 */3 * * *",
         "uprev": false,
         "useflags": [
@@ -1070,7 +1067,6 @@
         "doc": "https://dev.chromium.org/chromium-os/build/builder-overview#TOC-Continuous",
         "hw_tests_override": null,
         "luci_builder": "Try",
-        "manifest_branch": "main",
         "useflags": [
             "-chrome_internal"
         ]
@@ -1412,7 +1408,6 @@
         "doc": "https://dev.chromium.org/chromium-os/build/builder-overview#TOC-Continuous",
         "hw_tests_override": [],
         "luci_builder": "Informational",
-        "manifest_branch": "main",
         "schedule": "0 */3 * * *",
         "uprev": false,
         "vm_tests": []
@@ -1459,7 +1454,6 @@
         "doc": "https://dev.chromium.org/chromium-os/build/builder-overview#TOC-Continuous",
         "hw_tests_override": null,
         "luci_builder": "Try",
-        "manifest_branch": "main",
         "vm_tests": []
     },
     "amd64-generic-unittest-stress": {
@@ -4060,7 +4054,6 @@
         "hw_tests_override": [],
         "internal": true,
         "luci_builder": "Informational",
-        "manifest_branch": "main",
         "manifest_repo_url": "https://chrome-internal-review.googlesource.com/chromeos/manifest-internal",
         "overlays": "both",
         "uprev": false,
@@ -4080,7 +4073,6 @@
         "hw_tests_override": null,
         "internal": true,
         "luci_builder": "Try",
-        "manifest_branch": "main",
         "manifest_repo_url": "https://chrome-internal-review.googlesource.com/chromeos/manifest-internal",
         "overlays": "both",
         "vm_tests": []
@@ -8143,7 +8135,6 @@
             "factory_install"
         ],
         "luci_builder": "Full",
-        "manifest_branch": "main",
         "prebuilts": "public",
         "schedule": "with 30m interval",
         "use_sdk": false,
@@ -8237,7 +8228,6 @@
             "factory_install"
         ],
         "luci_builder": "Try",
-        "manifest_branch": "main",
         "prebuilts": "public",
         "use_sdk": false,
         "usepkg_build_packages": false,