This reverts commit 4c67f856.

Reason for revert: crbug.com/1200657

Original change's description:
> git-cache: Add option to fetch commits.
>
> Add option to git cache to fetch commits.
> And use it in bot_update and gclient sync to make sure
> the needed commits are present on the checkout.
>
> Change-Id: I9e90da9e3be6e7bacf714b22bf0b735463e655b6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2829942
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

Change-Id: I31a1defb26119bcb46894ab4084d626b65c45fed
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2837413
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>