emacs: Allows non-x11 build on distribution supporting x11

By default emacs will build with x11 if the distribution has x11
support. However in a .bbappend file a user could strip away x11
support, even if x11 is supported on the platform. There was another
check in do_compile_prepend() that checked if the distro has x11
feature and not if PACAKAGECONFIG enables x11 support.

Since in this receipe dbus dependence is only marked if x11 is
enabled, desactiving x11 support should also desactivate dbus support.

Signed-off-by: Alexandre Tuleu <alexandre.tuleu.2005@polytechnique.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>