Revert of implement device::clear until we can remove callers in chrome skia/ext (patchset #1 id:1 of https://codereview.chromium.org/773903002/)

Reason for revert:
failing win unittests

Original issue's description:
> implement device::clear until we can remove callers in chrome skia/ext
>
> BUG=skia:
> TBR=
>
> Committed: https://skia.googlesource.com/skia/+/252fccfb546efe83fb1d2c7a0b3c18a96ff46ea4

TBR=reed@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/774063002
1 file changed