Remove WallTimer class.

Only used in three somewhat dubious places.

Change-Id: I7ccd1aef41f826d0eb62606751f4d3f0ceda267d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/227065
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
6 files changed