Impl.getNameOf() no longer makes methods unprunnable.

A recent patch marked methods referred to by Impl.getNameOf so that
they are not inlined, devirtualized or prunned. Marking them as non
prunnable is not really necessary for our current use cases, and
Impl.getNameOf() documentation already states that it will return
null for prunned methods.

Change-Id: Ieedbece696d0d0132022483548b1bb99992fd3b4