Revert "Reland "GPU support for SkMixers""

This reverts commit c9822a1818ba8fe91dbea28e592fd18034899e3e.

Reason for revert: got it

Original change's description:
> Reland "GPU support for SkMixers"
> 
> This reverts commit e6ebe7427a0e0d6a42d3d7ef1b2575c0d29c96e1.
> 
> Reason for revert: want to see the breaks
> 
> Original change's description:
> > Revert "GPU support for SkMixers"
> > 
> > This reverts commit 3f2d05e7af2f0774f987f8fdf10c7c0c05079f5b.
> > 
> > Reason for revert: breaking the bots
> > 
> > Original change's description:
> > > GPU support for SkMixers
> > > 
> > > Bug: skia:
> > > Change-Id: Ic92f0b3c4613b3d599d59924d93cd4da8d161e89
> > > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204445
> > > Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> > > Reviewed-by: Mike Reed <reed@google.com>
> > > Reviewed-by: Brian Salomon <bsalomon@google.com>
> > 
> > TBR=bsalomon@google.com,ethannicholas@google.com,reed@google.com
> > 
> > Change-Id: Ice7c470a57a3ae55215288718aa6390592bd85e5
> > No-Presubmit: true
> > No-Tree-Checks: true
> > No-Try: true
> > Bug: skia:
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204724
> > Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
> > Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> 
> TBR=bsalomon@google.com,ethannicholas@google.com,reed@google.com
> 
> Change-Id: If51303bc320fc488196ef9e696df8480bfbd31f6
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: skia:
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204962
> Reviewed-by: Mike Reed <reed@google.com>
> Commit-Queue: Mike Reed <reed@google.com>

TBR=bsalomon@google.com,ethannicholas@google.com,reed@google.com

Change-Id: I509687bcfe8fde6760b74c566e4405ff12f9cc9e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204963
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
14 files changed