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>

command.py

@@ -476,8 +476,7 @@ class Command:
             top = self.manifest
         yield top
         if not opt.this_manifest_only:
-            for child in top.all_children:
-                yield child
+            yield from top.all_children
 
 
 class InteractiveCommand(Command):