This reverts commit 1b5328e0.

This commit has some pretty negative consequences with block copy. I
need to be able to force block copy on for arbitrary sequences while it
is still in development, and I need to be able to keep the palette
enable status between block copy and non-block copy runs.

Change If815a1eff2f9419117477f14cda143dd669c87c6 will prevent
allow_screen_content_tools from getting clobbered and still allow us to
force it on.
BUG=aomedia:656

Change-Id: I7a2f4207b5d2da35aec7870250e8b330c58a0e13