merge AbstractListener into CommonListener

since CommonListener is the only subclass

Change-Id: If10ccb29991d7c48e2c20fc41330572a669f1497
Reviewed-on: https://gerrit.libreoffice.org/13094
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>