remove xvfb from sheriff-o-matic makefile
remove xvfb from sheriff-o-matic makefile

BUG=404414
R=ojan@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/483773004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@180484 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs