Remove GrSurface-based surfaceContext factories from GrContextPriv

This relies on both:
   https://skia-review.googlesource.com/c/13001/ (Rm makeRenderTargetContext in favor of deferred version)
   https://skia-review.googlesource.com/c/11125/ (Remove discard from GrRenderTarget & force it to always go through a RenderTargetContext)

Change-Id: Ia06469a6fa0048e162fb769ed4a11e4773cfacca
Reviewed-on: https://skia-review.googlesource.com/13130
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
4 files changed