Remove gpu configs that don't have explicit API.

Remove gpu configs that don't have explicit API.

DOCS_PREVIEW= https://skia.org/?cl=9871

Change-Id: I510473cf91d8bee38d1e33424b1ae7b30dc86968
Reviewed-on: https://skia-review.googlesource.com/9871
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>