This deprecates --exhaustive-variants and --no-variants flags to
simplify code configuring variants.

Simplification after:
https://crrev.com/c/789831

Bug: chromium:788104
Change-Id: Ie77d48eca083e7721e02d34bc1e9aa1b1f0d0202
Reviewed-on: https://chromium-review.googlesource.com/789836
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49633}