Fuse GrReplacements and GrLayerCache

The conversion step from GrCachedLayer to ReplacementInfo isn't necessary.

Review URL: https://codereview.chromium.org/769533004
(re)baseline several of my gms

TBR=
NOTRY=true

Review URL: https://codereview.chromium.org/780593002
Remove unused constants.

BUG=skia:

Review URL: https://codereview.chromium.org/773193004