signal fix

You remove the signal twice from the event loop:
- once manually with GMain.Idle.remove
- once implicitly by returning false from the callback ( https://developer.gnome.org/glib/stable/glib-The-Main-Event-Loop.html#g-idle-add )

With newer versions of glib, this triggers warning messages (See https://github.com/GNOME/glib/commit/a919be3d39150328874ff647fb2c2be7af3df996 )