remove the GPU checkbox from the hash / database

We decided last week that GPU rendering wouldn't be associated
with the fiddle itself; options in the left bar will be split into
ones that are bound to the fiddle (so appear in the hash and database)
and ones that are run-specific (like the rendering mode).

This will leave us better placed to do things like rendering in multiple
modes at once.

BUG=skia:
R=jcgregorio@google.com

Review URL: https://codereview.chromium.org/685543002
4 files changed