Remove unnecessary macros from SkString header.

They have been replaced with equivalent constants (and given the
requisite k prefix).

Change-Id: I70907eec234e0861cc97aac1ca03086faca42f9a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/306160
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
6 files changed