enter_chroot: disable depot_tools updates inside the SDK

We update the depot_tools checkouts ourselves through our manifest,
so there's no need or desire for this code to try and manage it.

BUG=chromium:1166896
TEST=CQ passes

Change-Id: I8048fd2e5f30f4d4c512a47118e07c799d63e075
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2631045
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
diff --git a/sdk_lib/enter_chroot.sh b/sdk_lib/enter_chroot.sh
index 5199de5..1f7b8b3 100755
--- a/sdk_lib/enter_chroot.sh
+++ b/sdk_lib/enter_chroot.sh
@@ -695,6 +695,9 @@
   # The default ~/.bash_profile in chroot will cd to $CHROOT_CWD instead of
   # ~/trunk/src/script if that environment variable is set.
   "CHROOT_CWD=${FLAGS_working_dir}"
+
+  # We don't want to auto-update depot_tools inside of the SDK as we manage it.
+  "DEPOT_TOOLS_UPDATE=0"
 )
 
 # Needs to be set here because setup_env runs in a subshell.