gsutil: use os.path.expanduser

Makes the code a little simpler and avoids relying on the env directly.

Bug: b/285376658
Change-Id: Iae8300059b3418e0a9224eb555df6eb6cafa9437
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4582288
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>

recipes/recipe_modules/gsutil/resources/gsutil_smart_retry.py

@@ -53,7 +53,7 @@ def main(argv):
     # Failed at least once, try deleting the tracker files
     try:
       logging.warning('Trying harder: deleting tracker files')
-      gsutil_dir = os.path.join(os.environ['HOME'], '.gsutil')
+      gsutil_dir = os.path.expanduser('~/.gsutil')
       logging.info('Removing %s' % gsutil_dir)
       shutil.rmtree(gsutil_dir)
     except BaseException as e: