Revert "Move some Gr headers from include/gpu to include/private and src/gpu."

This reverts commit 3bdc3f5f9c0bf62c1eb7932f67f9f4838782a36a.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Move some Gr headers from include/gpu to include/private and src/gpu.
> 
> Bug: skia:
> Change-Id: I341dd3bff63cc99d3be830e21673073645a9cfec
> Reviewed-on: https://skia-review.googlesource.com/c/176220
> Auto-Submit: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>

TBR=bsalomon@google.com,robertphillips@google.com

Change-Id: Ia7082f66abb969b20dd5d1f12c3c8d09cd84c241
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/c/176587
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
9 files changed