Remove "www.last.fm" keyword from overheard

Currently the overheard is catching a lot of twits about people sending the last song they played. Not very useful and it spams the stream which means that people (like me) monitoring for people twitting for help, cannot find it (I won't even register to last.fm overheard when 95% is last song played spam)

This can be fixed by excluding the keyword www.last.fm. Since most automated scripts send the full url of the artist (which is what is being caught), by removing this keyword, only twits actually wiring "last.fm" will be shown

See the difference for yourself