Remove useless android-changed comments.

I've changed useful ones to regular comments or TODOs, as appropriate.

I've left ones in code like java.util.concurrent where we really are
tracking an upstream source, making the change markers useful.

I've left a handful of others where I intend to actually investigate
the implied TODOs before deciding how to resolve them.

Change-Id: Iaf71059b818596351cf8ee5a3cf3c85586051fa6
120 files changed