Eliminate SkVM-specific features from Viewer.

SkVM is being removed; we no longer need SkVM command line flags and
ImGui views.

Change-Id: Ief70ce5df702be87ef1c4ee2177dfc0e0d863fca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/678436
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Nicolette Prevost <nicolettep@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
2 files changed