Return to previous RenderEngine behavior for protected buffers

This reverts to the old RenderEngine behavior of not keeping
protected buffers bound as GPU textures. Doing so cause us to
bind the buffer to a GPU texture every frame, but prevents us
from exhausting the protected resources.

Test: atest com.google.android.media.gts.WidevineDashPolicyTests
Bug: 187870007
Change-Id: I5cc95d47fbc0bdfa239fe99dd479aef5c87c0495