This reverts commit fc9a40e3.

Reason for revert: at least one tryjob if failing:
Gerrit Plugins Tester

Original change's description:
> Reland "Add support for Gerrit topics in gclient syncs"
>
> This is a reland of 0f13273f
>
> Hopefully the cause of the original revert was fixed in https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3480835
>
> Original change's description:
> > Add support for Gerrit topics in gclient syncs
> >
> >
> > If the new flag "--download-topics" is specified with a "--patch-ref" then:
> > * Finds the topic of the Gerrit change.
> > * Finds all open changes in the same repo as the Gerrit change.
> > * Cherrypicks all changes locally.
> >
> > This functionality can be used by developers and bots to apply all changes with the same topic in the checkout to be tested at the same time (similar to how Android's TreeHugger handles topics).
> >
> >
> > Tested by:
> >
> > * Running the new unit test with `python gclient_scm_test.py GerritChangesTest.testDownloadsTopics` from the `tests/` directory.
> >
> > * Running an end-to-end test with `DEPOT_TOOLS_UPDATE=0 gclient sync --patch-ref "skia@d831da5b8ac2d257c5b0cf2ec6645a148f05e662:refs/changes/17/505217/2" --download-topics` in a skia checkout.
> >
> >
> > Bug: chromium:1298922
> > Change-Id: Ieace5e27fbc9c5d0ea90a037bf80a95062c1b164
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3444003
> > Reviewed-by: Josip Sokcevic <sokcevic@google.com>
> > Commit-Queue: Ravi Mistry <rmistry@chromium.org>
>
> Bug: chromium:1298922
> Change-Id: I80747d797234bba06c17ef5c5e85b310281922c4
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3484976
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>
> Commit-Queue: Ravi Mistry <rmistry@chromium.org>

Bug: chromium:1298922
Change-Id: I845321941157ab55d026488b7ce59787ba5e57f2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3488245
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>