minor skvm cleanup

This is just minor little stuff I've been meaning to do,
with essentially no impact anywhere.

   - Add an easy-to-flip switch to disable the JIT.

   - Stop checking so carefully whether we hasJIT()
     in test_jit_and_interpreter().  This was helpful
     for making progress but now just gets in the way.

Change-Id: I08065ba1f42700f9d7d63f8303af357ec5fe11ae
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302944
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
2 files changed