Unpin cros_sdk repositories.

During the transition, let's unpin cros_sdk repositories to keep COS
repos as closely in sync with ChromeOS repos as possible. This will
simplify the release of changes that COS developers make to cros_sdk
repositories during the transition. Additionally, this will simplify the
Vomit transition, since the package set being monitored will match
exactly between COS and ChromeOS.

BUG=b/157698755
TEST=sync and build

Change-Id: I3617d60a4a79cecede9d35dd48086e93bb29c143
diff --git a/external_full.xml b/external_full.xml
index 81d0c74..c41bec4 100644
--- a/external_full.xml
+++ b/external_full.xml
@@ -25,63 +25,47 @@
 
   <!-- mirrored cros_sdk dependencies -->
   <project path="src/third_party/portage-stable"
-           name="mirrors/cros/chromiumos/overlays/portage-stable"
-           revision="daba3b445d5606919ccbc7351b0a86088dcea887" />
+           name="mirrors/cros/chromiumos/overlays/portage-stable" />
   <project path="chromite"
-           name="mirrors/cros/chromiumos/chromite"
-           revision="cdc46f3f2562203fd357360e470cca07b418802b" />
+           name="mirrors/cros/chromiumos/chromite" />
   <project path="chromite/infra/proto"
-           name="mirrors/cros/chromiumos/infra/proto"
-           revision="4f211148aa5885eb8fb8e7fa402a71d9a775ff55" />
+           name="mirrors/cros/chromiumos/infra/proto" />
   <project path="chromite/third_party/pyelftools"
            name="mirrors/cros/chromiumos/third_party/pyelftools"
-           revision="0890b98431a9b2e637c18f719232d06a4e5c3cd8" />
+           revision="refs/heads/master-0.22" />
   <project path="src/platform/crostestutils"
-           name="mirrors/cros/chromiumos/platform/crostestutils"
-           revision="4580b7328b7dc4dd9953bec17c102efefbe0a165" />
+           name="mirrors/cros/chromiumos/platform/crostestutils" />
   <project path="src/scripts"
-           name="mirrors/cros/chromiumos/platform/crosutils"
-           revision="4b0910420ec2d0f9880dc02d63f95a50bd891c15" />
+           name="mirrors/cros/chromiumos/platform/crosutils" />
   <project path="src/platform/vboot_reference"
-           name="mirrors/cros/chromiumos/platform/vboot_reference"
-           revision="7ea99225b562b49b30fc374065f9dd48ed52f70d" />
+           name="mirrors/cros/chromiumos/platform/vboot_reference" />
   <project path="src/third_party/autotest/files"
-           name="mirrors/cros/chromiumos/third_party/autotest"
-           revision="9c71d39c859c282f41e7897535eb97467852da86" />
+           name="mirrors/cros/chromiumos/third_party/autotest" />
   <project path="src/third_party/chromiumos-overlay"
            sync-c="true"
-           name="mirrors/cros/chromiumos/overlays/chromiumos-overlay"
-           revision="d76a24fef946b13e3faddb354bc8b24804ae45d1" />
+           name="mirrors/cros/chromiumos/overlays/chromiumos-overlay" />
   <project path="src/third_party/eclass-overlay"
-           name="mirrors/cros/chromiumos/overlays/eclass-overlay"
-           revision="261a04be814201bd5a99b459f48ee7c3ad084589" />
+           name="mirrors/cros/chromiumos/overlays/eclass-overlay" />
   <project path="src/platform/dev"
-           name="mirrors/cros/chromiumos/platform/dev-util"
-           revision="ad4a48310d060d983c968352a04b92494c3f09e0" />
+           name="mirrors/cros/chromiumos/platform/dev-util" />
   <project path="src/platform/verity"
-           name="mirrors/cros/chromiumos/platform/dm-verity"
-           revision="393cd4d510256b0bb2bdd0acd9656105cfd28771" />
+           name="mirrors/cros/chromiumos/platform/dm-verity" />
   <project path="src/third_party/toolchain-utils"
-           name="mirrors/cros/chromiumos/third_party/toolchain-utils"
-           revision="a5ec48569265998036527fcfeb94c1f9c1e314a3" />
+           name="mirrors/cros/chromiumos/third_party/toolchain-utils" />
   <project path="src/third_party/portage_tool"
            name="mirrors/cros/chromiumos/third_party/portage_tool"
-           revision="dccf55ec9fc43c66af23097a9fc410ffe99d020a" />
+           revision="refs/heads/chromeos-2.3.75" />
   <project path="src/chromium/depot_tools"
-           name="mirrors/cros/chromium/tools/depot_tools"
-           revision="19d4809e112652f918494840bab819603b0a2816" />
+           name="mirrors/cros/chromium/tools/depot_tools" />
   <project path="src/third_party/coreboot"
            name="mirrors/cros/chromiumos/third_party/coreboot"
-           revision="e1312db872cec1289a9f7f0bb19a08ae582b959a" />
+           revision="refs/heads/chromeos-2016.05" />
   <project path="src/third_party/modp_b64"
-           name="mirrors/cros/aosp/platform/external/modp_b64"
-           revision="ae26ad8516036774fd3b6e84a98a89955dcf5f61" />
+           name="mirrors/cros/aosp/platform/external/modp_b64" />
   <project path="src/platform2"
-           name="mirrors/cros/chromiumos/platform2"
-           revision="e975e83bb24b0f21bffe2a5f1c630279b8e445f1" />
+           name="mirrors/cros/chromiumos/platform2" />
   <project path="src/repohooks"
-           name="mirrors/cros/chromiumos/repohooks"
-           revision="69d3e18502d1cb317938ab86cf94aba2ee8e608f" />
+           name="mirrors/cros/chromiumos/repohooks" />
 
   <!-- COS sources -->
   <project path="src/overlays"