aidl_interface: check frozen APIs against ToT

This also drops support for recognizing an empty directory as an API freeze
since this adds complication and it is no longer required now that the
directory is created automatically.

Bug: 121051028
Test: manual:
 - error on change to frozen API
 - error on change to ToT for frozen API
 - try freezing API of a module

Change-Id: I51a6a4bb57bae51ba03e7faac34e1b3e0af49fb3
1 file changed