cleanup: leverage yield from in more places

Change-Id: I4f9cb27d89241d3738486764817b51981444a903
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/390274
Reviewed-by: Aravind Vasudevan <aravindvasudev@google.com>
Commit-Queue: Mike Frysinger <vapier@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

platform_utils.py

@@ -193,10 +193,9 @@ def _walk_windows_impl(top, topdown, onerror, followlinks):
     for name in dirs:
         new_path = os.path.join(top, name)
         if followlinks or not islink(new_path):
-            for x in _walk_windows_impl(
+            yield from _walk_windows_impl(
                 new_path, topdown, onerror, followlinks
-            ):
-                yield x
+            )
     if not topdown:
         yield top, dirs, nondirs