project.config: grant removeLabel-TryBot-Result to everyone who can run TryBots

Gerrit changed so that this permission is not implicitly granted by Remove Reviewer.

Change-Id: I4426f6b14540dc2a6332e2249e779c978fb60a8b
Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/461815
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>