Remove SkLights include from SkCanvas.h

SkLights.h pulls in a bunch of other headers and is not needed (fwdecl
works fine).

Change-Id: Id2d7176eb3bf4609f72f46d513eebf59318f542f
Reviewed-on: https://skia-review.googlesource.com/14904
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
46 files changed