Remove redundant backslashes

fleka8 reports:

  E502 the backslash is redundant between brackets

Fixed automatically with autopep8:

  git-repo $ git ls-files | grep py$ | xargs autopep8 --in-place --select E502

Change-Id: I1486ae1d17206918474363daf518274c5be8daed
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/254602
Tested-by: David Pursehouse <dpursehouse@collab.net>
Reviewed-by: Mike Frysinger <vapier@google.com>