Remove generated java source post clean logic

Just move the proto and renderscript sources into their own directories
-- the entire directory is wiped if the file list changes since the
command line will change. So we can just enable/disable pulling sources
from those directories based on whether there were files in the list or
not.

Bug: 30947985
Test: m -j java
Test: Remove a proto file from a java lib, ensure the generated source
      is not included.
Change-Id: If7529979de6fa62a651933a3a974f47b033851d6