[win-bootstrap] Remove use-system-git flag

Bug: b/360206460
Change-Id: I1654c4cce2da4bd53df90ffdfc13c4f7336ab975
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6171042
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
Commit-Queue: Anne Redulla <aredulla@google.com>

bootstrap/bootstrap.py

@@ -483,11 +483,6 @@ def main(argv):
     parser.add_argument('--bootstrap-name',
                         required=True,
                         help='The directory of the Python installation.')
-    parser.add_argument(
-        '--use-system-git',
-        action='store_true',
-        help='Whether to prefer a direct git installation over a depot_tools '
-        'bundled git.')
     args = parser.parse_args(argv)
 
     logging.basicConfig(level=logging.DEBUG if args.verbose else logging.WARN)
@@ -505,9 +500,7 @@ def main(argv):
     if IS_WIN:
         # Avoid messing with system git docs.
         add_docs = False
-        git_dir = None
-        if args.use_system_git:
-            git_dir = search_win_git_directory()
+        git_dir = search_win_git_directory()
         if not git_dir:
             # Either using system git was not enabled
             # or git was not found in PATH.

bootstrap/win_tools.bat

@@ -52,7 +52,7 @@ if "%PYTHON3_VERSION%" == "" (
 :: Python is upgraded.
 set BOOTSTRAP_NAME=bootstrap-%PYTHON3_VERSION:.=_%_bin
 set BOOTSTRAP_PATH=%BOOTSTRAP_ROOT_DIR%\%BOOTSTRAP_NAME%
-set BOOTSTRAP_EXTRA_ARGS=--bootstrap-name "%BOOTSTRAP_NAME%" --use-system-git
+set BOOTSTRAP_EXTRA_ARGS=--bootstrap-name "%BOOTSTRAP_NAME%"
 
 :: Install our CIPD packages. The CIPD client self-bootstraps.
 :: See "//cipd.bat" and "//.cipd_impl.ps1" for more information.