Remove some legacy GN defines for Flutter

Flutter's code has been updated so these can all be removed

Change-Id: Id3b778158fce175efd23b80a1d1245106c848501
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/279840
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed