Some cleanup of GrSwizzle

public before private
some c++14 constexprification
remove unused functions

Change-Id: Idb49c476020c7fe9be624fc21c1371e99bf22bb1
Reviewed-on: https://skia-review.googlesource.com/c/162821
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed