core: Explicitly remove bus watch
core: Explicitly remove bus watch

We need to do this to break cyclic reference between HTTPGstResponse,
GstPipeline and GstBus.

GNOME/rygel,Tarnyko/rygel,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,Pelagicore/Media-Manager-Rygel-patched,Pelagicore/Media-Manager-Rygel-patched,GNOME/rygel,Tarnyko/rygel,jku/rygel,jku/rygel,luisbg/rygel