Rename SkTDArray::pop -> pop_back

There are a few instances where a parameter was passed to pop. I
changed those to use back() and pop_back().

Change-Id: Ie93ad55830bae074af7cb6c92c445f01c20c90b2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/586285
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Herb Derby <herb@google.com>
19 files changed