[win-bootstrap] Cleanup update_depot_tools.bat for lack of git-for-windows

Bug: b/360206460
Change-Id: I1a4d9ac8a4e0f19356e22bc15a664cc838e52cd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6205947
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Anne Redulla <aredulla@google.com>

update_depot_tools.bat

@@ -34,16 +34,13 @@ IF "%DEPOT_TOOLS_UPDATE%" == "0" GOTO :EOF
 
 echo Updating depot_tools...
 
-:: Download git for the first time if it's not present.
+:: Test git is installed by checking its version.
 call git --version > nul 2>&1
-if %ERRORLEVEL% == 0 goto :GIT_UPDATE
-call "%DEPOT_TOOLS_DIR%bootstrap\win_tools.bat"
-if errorlevel 1 (
-  echo Error updating depot_tools, no revision tool found.
+if %ERRORLEVEL% NEQ 0 (
+  echo Git isn't installed. Please install it.
   exit /b %ERRORLEVEL%
 )
 
-:GIT_UPDATE
 :: Now clear errorlevel so it can be set by other programs later.
 set errorlevel=
 
@@ -65,5 +62,5 @@ if errorlevel 1 (
 :: Sync CIPD and CIPD client tools.
 call "%~dp0\cipd_bin_setup.bat"
 
-:: Update git and python.
+:: Update python.
 call "%DEPOT_TOOLS_DIR%bootstrap\win_tools.bat"