Remove ui/gfx/screen_type_delegate.h

This removes gfx::SCREEN_TYPE_NATIVE/SCREEN_TYPE_ALTERNATE, and there is
now only one Screen instance. It's still a runtime-installed thing for
test purposes.

TBR=various owners for trivial changes
R=oshima@chromium.org, sky@chromium.org
BUG=558054

Review URL: https://codereview.chromium.org/1608733002

Cr-Commit-Position: refs/heads/master@{#371676}
152 files changed