Remove SkSafeSetNull.

Update all users to sk_sp.

Change-Id: I6453b9456b9a8f9e2b756381797f1382ef9e6561
Reviewed-on: https://skia-review.googlesource.com/141052
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Herb Derby <herb@google.com>
11 files changed