upload: drop check for uncommitted local changes

git push, like most git commands, does not warn or otherwise prompt
users when there are local uncommitted changes.  To simplify the
upload logic, and to harmonize repo upload with git push as a more
git-esque flow, stop checking/warning/prompting the user here too.

Change-Id: Iee18132f0faad0881f1a796cb58821328e04b694
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/425337


Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Mike Frysinger <vapier@google.com>