Remove bits of code related to sk_Args

AFAICT, there were two unrelated things happening here:

1) .fp files supported referencing class variables as if they existed in
   sk_Args. We never do this (they can be directly referenced).
2) When baking the values of 'in' variables into runtime SkSL, we
   generated intermediate 'Setting' objects that wrapped the literal
   values supplied by the user. Those Setting objects were named
   'sk_Args.<field_name>', even though this logic had nothing to do with
   the fake SkArgs type. In this case, the Setting objects don't appear
   to add any value, so just inject the literals directly (which is what
   constant propagation would do on the next iteration).

Change-Id: Ia54193c5282737653cf10b7aae77e38e5ab78c79
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/307793
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
4 files changed