Remove "unlinklib" command from installd

unlinklib is no longer necessary since libraries are now either stored
in an ASEC container or in /data/app-lib

Replace lib directory with a symlink to the /data/app-lib directory even
if it's a dangling link. That way developers don't name something "lib"
in their directory which gets blown away during an update.

Change-Id: I142cf13dba9c13aafbaf0ff8d5e9872cbf1cc910