Remove unused ui_simple_dialog.h from qt Makefile.common

Change-Id: I366a52a037462cb059565365ea1eec5be228078f
Reviewed-on: https://code.wireshark.org/review/5475
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>