Consolidate all the destroy all loops into clear()

Use clear() to clean up a common code pattern.

Change-Id: I372227f068f9bc50b6e533e103e604b487654be4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/600159
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
1 file changed