Remove DIRTY_DISSECTOR_SRC

x11 dissector don't have longer warning !
and fix different between Autotools and CMake (about gsm_a_common dissector)

Change-Id: Id9da62d84b8b0bb4b0ed5d8fc62abba4e2442ed2
Reviewed-on: https://code.wireshark.org/review/4621
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>