[backend] call correct function
    
    addressing:
    Traceback (most recent call last):
      File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
        self.run()
      File "/usr/share/copr/copr-be.py", line 86, in run
        self.fetch_jobs()
      File "/usr/share/copr/copr-be.py", line 76, in fetch_jobs
        ao.run()
      File "/usr/share/copr/backend/actions.py", line 29, in run
        self.events('Removing %s' % path)
    TypeError: 'Queue' object is not callable