Convert the aac audio format handler to libmp4ff.

Convert the aac audio format handler to libmp4ff.

This changes the aac audio format handler to call the primitives
provided by the mp4ff library. This allows to remove the atom parsing
code from aac_afh.c.

After this change para_server, para_afh, and para_recv no longer
depend on aac_common.c and on the mp4v2 library.  The autoconf tests
for libmp4v2 are removed from configure.ac. A subsequent commit will
deal with aac_common.c.