Remove SkTDArray::isEmpty

Change-Id: I82f5dee23247dbd445284fa5d1c5d812c4014a47
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/584224
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Herb Derby <herb@google.com>
11 files changed