All dependencies that are in common_ss (which includes system_ss) automatically
have their include path added when building the target-specific files. So the
hack in ui/meson.build is not needed anymore since commit 727bb5b477 ("meson:
pick libfdt from common_ss when building target-specific files", 2024-05-10);
drop it.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>