We updated git client to 2.21, so let's use git protocol version 2.

Bug: 875453
Change-Id: I5bd12c5fdcd4b87a067e5c85dd9c464e5d3bade9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1534211
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>