Cleanup TODO for constant-expression handling.

Support for constant-expression function calls in SkSL now exists, and
support for abs() was added at http://review.skia.org/405676.

Change-Id: I3144af993db93a3d640971734d4cb03e0cfb8589
Bug: skia:10835
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/408642
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed