An issue exists with reference_masking in non-rd pickmode for spatial
scaling. It was kept off for internal dynamic resizing and svc, this
change is to keep it off also for external dynamic resizing.

Update to external resize test, and update TODO to re-enable this
at frame level when references have same scale as source.

Change-Id: If880a643572127def703ee5b2d16fd41bdbf256c