Revert "Convert DstTexture to DstProxy"

Revert "Convert DstTexture to DstProxy"

This reverts commit 87f7f1c3ce519115141b40f1d8faede437c8f357.

Reason for revert: grumble, grumble

Original change's description:
> Convert DstTexture to DstProxy
>
> The last GrTexture-based TextureSampler::reset call must be removed before the TextureSamplers can become purely GrTextureProxy-backed
>
> Split out of: https://skia-review.googlesource.com/c/10484/ (Omnibus: Push instantiation of GrTextures later (post TextureSampler))
>
> Change-Id: Ic1435177d8b5d9bd3fc38b4903c9baae8205cfb0
> Reviewed-on: https://skia-review.googlesource.com/16908
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>
>

TBR=egdaniel@google.com,robertphillips@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I9af52bb222bd2d8cc696250a9efb62afb80edba1
Reviewed-on: https://skia-review.googlesource.com/17203
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>