Revert of Add OpenGL context to Viewer. (patchset #7 id:120001 of https://codereview.chromium.org/1978573003/ )

Reason for revert:
sk_app/WindowContext.cpp is missing. Need to add file and resubmit.

Original issue's description:
> Add OpenGL context to Viewer.
>
> BUG=skia:
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1978573003
>
> Committed: https://skia.googlesource.com/skia/+/56a11e4d6f3d436a3c2497c9c9e71a117d78a93f

TBR=brianosman@google.com,bsalomon@google.com,djsollen@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review-Url: https://codereview.chromium.org/1990893002
19 files changed