Revert "Make depot_tools scripts return exit codes properly on all platforms."

This reverts commit 7c4f7ec408.

Reason for revert: bugs reported by users (see comments in Gerrit).
error: block. was unexpected at this time.

Original change's description:
> Make depot_tools scripts return exit codes properly on all platforms.
>
> Changes:
> 1. Windows: exit /b %errorlevel% should be used instead of goto :EOF to get valid exit codes during cmd /c <script>.bat invocation.
> 2. Windows: delayed var expansion is required in update_depot_tools.bat exit code generation.
> 3. Posix: update_depot_tools returns exit code from update_git_repo function in case of a failure.
>
> A rule of thumb on Windows: goto :EOF should not be used if %errorlevel% must be returned for all possible invocations.
>
> Test case for update_depot_tools changes:
> 1. Make a change to depot_tools sources that will conflict with next depot_tools update
> 2. Run update_depot_tools either directly or via gclient
> 3. Expect a git error is triggered
> 4. Inspect %errorlevel% or $? depending on platform
> 5. Expected 1, but the actual result is 0.
>
> Test case for changes in other .bat files:
> 1. Make a change to depot_tools sources that will conflict with next depot_tools update
> 2. Run cmd /c gclient
> 3. Expect a git error is triggered
> 4. Inspect %errorlevel%
> 5. Expected 1, but the actual result is 0.
>
> Change-Id: I64459982bcd9cc3db1319a9b39224b7a7af8c5aa
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3688632
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>
> Auto-Submit: Aleksey Khoroshilov <akhoroshilov@brave.com>
> Reviewed-by: Bruce Dawson <brucedawson@chromium.org>

Change-Id: I85d598af01d75588cdee77165d6af22270ee031d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3694139
Auto-Submit: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>

update_depot_tools

@@ -129,11 +129,7 @@ if [ "X$DEPOT_TOOLS_UPDATE" != "X0" ]; then
   if [ -e "$base_dir/.git" ]; then
     cd "$base_dir"
     update_git_repo
-    UPDATE_RESULT=$?
     cd - > /dev/null
-    if [[ $UPDATE_RESULT -ne 0 ]]; then
-      exit $UPDATE_RESULT
-    fi
   fi
 
   # Sync CIPD-boostrapped packages.