remove Builder inheritance

With all those new toys it's just as clear to use skvm::Builder
without inheriting from it.

Change-Id: I105973db465d889ded528f476a479232f6e70391
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/280335
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed