Also, rename --all-files to --all_files to be consistent with other
options, and remove reviewers, since it's never set in presubmit_support.

Bug: 1042324
Change-Id: I34fa3162c56e39bcdd52ad1e19058357de934f1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2067351Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>