network-manager-applet: remove polkit-gnome dependency and un-blacklist recipe

* polkit-gnome caused blacklisting
* upstream dependency on polkit-gnome was removed in:
  | commit 0f378cce475b136bb1c6124bc2ea803e1da7dfc8
  | Author: Dan Williams <dcbw@redhat.com>
  | Date:   Fri Mar 2 14:07:31 2012 -0600

  |  build: remove unused polkit configure check

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>