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
Revert "Change clear() to respect the clip"

This reverts commit 3729469d6a12266037b697c2192768545e097ab0.

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/778563002
Revert of rebaseline after clear change -- pdf was not treating clear as SRC_MODE (patchset #1 id:1 of https://codereview.chromium.org/759303004/)

Reason for revert:
reverted clear() change

Original issue's description:
> rebaseline after clear change -- pdf was not treating clear as SRC_MODE
>
> BUG=skia:
> NOTRY=True
> TBR=
>
> Committed: https://skia.googlesource.com/skia/+/2fb352abebc342a322d4a66c054bbff8bd565767

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

Review URL: https://codereview.chromium.org/774073002