Update list of builders that garden-o-matic uses.

There are no longer any Perf builders on the chromium.webkit
waterfall and the Oilpan builders are not the responsibility
of the Blink gardeners to maintain.

NOTRY=true

Review URL: https://codereview.chromium.org/272213003

git-svn-id: svn://svn.chromium.org/blink/trunk@173919 bbb929c8-8fbe-4397-9dbb-9b2b20218538