isolated_app: remove app_data_file execute

In commit ad891591, we allowed
isolated processes to execute files from /data/data/APPNAME.

I'm pretty sure all the necessary linker changes have been made
so that this functionality isn't required anymore. Remove the
allow rule.

This is essentially a revert of ad891591.

Change-Id: I1b073916f66f4965dfc53c0ea2b624bbb2fe8816