Remove RTF and MP3 parse plugins

Parse-rtf and parse-mp3 are not built by default due to licensing issues. Since we now have parse-tika to handle these formats I would be in favour of removing these 2 plugins altogether to keep things nice and simple. The other plugins will probably be phased out only after the release of 1.1 when parse-tika will have been tested a lot more.

Any reasons not to?

Julien