Remove display() from compositing/ LayoutTests

This cleans up the remaining compositing/ display() calls, other than
two tricky cases (squash-animated-gif.html and
video-with-invalid-source.html) which are in different CLs for ease of
review and landing.

BUG=345027

Review URL: https://codereview.chromium.org/196653012

git-svn-id: svn://svn.chromium.org/blink/trunk@169478 bbb929c8-8fbe-4397-9dbb-9b2b20218538