Remove /release/, /work/ and /url/ from robots.txt.
MBS-5766: Re-add /url/ per discussion in ticket.

http://tickets.musicbrainz.org/browse/MBS-5766
Merge remote-tracking branch 'freso/MBS-5766' into beta

* freso/MBS-5766:
  MBS-5766: Re-add /url/ per discussion in ticket.
  Remove /release/, /work/ and /url/ from robots.txt.