Revert "RenderEngine: don't blur when using protected content"

This reverts commit 247b2418.

We've fixed the issue in other CLs, so now we no longer need the
workaround.

Bug: 244398863
Bug: 213116783
Fixes: 270314344
Fixes: 205516620
Fixes: 242266174
Test: manual (ExoPlayer)
Change-Id: I6a7033360840b5caf0b84b56df25a44d9c789988