remove SK_USE_SKVM_BLITTER

Control everything with gSkUseSkVMBlitter, and that via --skvm flags.

We aren't skipping sprite blitters on the bots because
they're using the #define instead of the --skvm flag.
Might as well go all-in on the runtime flag now that
we have it... no need for the custom build jobs.

Change-Id: I56e5b1a72fecfc505aee5a26de6ee58666880922
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/282124
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
9 files changed