remove deadcode from trackinfoobject

we stoped using XML in the database a long time ago
remove promotrack feature

As far as I can tell this was only used way back in 1.8. It is also
called deprecated in the build system
remove plugindownload code from dlfprefplaylist

that code was just commented and rellied on files that don't exist
anymore
Merge pull request #82 from kain88-de/deadcode

Remove dead code. (promo tracks, plugin downloader, etc.)