Revert "Make it easier to test rectangle textures by using createBackendTexture."

This reverts commit 4e37751693a793505b0070eb8121fba99247d098.

Reason for revert: breaking some mac test bots

Original change's description:
> Make it easier to test rectangle textures by using createBackendTexture.
> 
> Also allows internal creation of rectangle textures, only used by unit
> tests currently.
> 
> Previously GrContext::createBackendTexture() would ignore the request
> for RECTANGLE or EXTERNAL and always make 2D. Now it makes RECTANGLE if
> supported and always fails for EXTERNAL.
> 
> Change-Id: Iafbb3f5acddb37bfb8d39740f2590177a07dae78
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297472
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>

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

Change-Id: Ia14c60ae996757369f1711ec0851e199cbbd4157
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297812
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
9 files changed