Remove testing/buildbot/GENERATION_OWNERS.

This file is no longer referenced.

Bug: 662541
No-Try: True
Change-Id: I0cd0c3ae19c6084a406b64cc38d43b63331d4ae6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578066
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653015}

testing/buildbot/GENERATION_OWNERS

-# This is reserved for people that are comfortable with
-# generate_buildbot_json and how the waterfalls are being converted
-# over
-# 
-# TODO(crbug.com/662541) - Get rid of this file and fold it
-# back into //testing/buildbot/OWNERS once we've converted all of
-# the non-perf waterfalls to genearte_buildbot_json
-
-dpranke@chromium.org
-jbudorick@chromium.org
-kbr@chromium.org