Revert of Templatize SkToXXX. (patchset #2 id:20001 of https://codereview.chromium.org/1814153003/ )

Reason for revert:
Chrome does not yet have std::underlying_type.

Original issue's description:
> Templatize SkToXXX.
>
> Makes the checked cast in debug more correct, avoiding new
> warnings in vs2015.
>
> BUG=skia:4553
>
> Committed: https://skia.googlesource.com/skia/+/0be9e806af72b3e029e691eef5c891c90d3fd320

TBR=reed@google.com,mtklein@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:4553

Review URL: https://codereview.chromium.org/1820433002