decoder/mp4v2: remove because of incompatible license

libmp4v2 is licensed under MPL 1.1, which is incompatible with GPLv2.
Unfortunately, this means that we must remove the plugin.

More information can be found in the Debian bug report:

 http://bugs.debian.org/767504
lib/nfs/FileReader: include Compiler.h for "final" fallback
lib/nfs/Connection: cancel DeferredMonitor on disconnect

Fixes potential second mount attempt after the old connection to the
NFS server was shut down.