qemu: remove explicit but redundant native build dependencies
qemu-native was optionally depending on libxext-native if the DISTRO_FEATURES
included x11. This dependency was required back when we didn't build
libsdl-native and causes an undesirable relationship between DISTRO_FEATURES and
qemu-native.
As the dependency isn't required anymore, remove it.
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
