Remove layout(marker) from runtime effect SkSL

This is another strange, experimental feature that clutters the
implementation and isn't used by anyone (to my knowledge).

Change-Id: I538b7eca0cd28aab32f4739b23459731ade9105e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/398226
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
26 files changed