[recipes] Remove deprecated (ignored) --use-bootstrap flag
[recipes] Remove deprecated (ignored) --use-bootstrap flag

This has been ignored for a long time, and I'd like to get rid of it.

R=jchinlee@chromium.org, ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org

Change-Id: I240d59cc10a2882041ac2c8abfeb1894237516a6
Reviewed-on: https://chromium-review.googlesource.com/c/1407425
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools