Makefile: Drop bogus cleaning of $(ALL_SUBDIRS)/qemu-options.def

When commit df2943ba moved "rm -f qemu-options.def" from distclean
to clean, it also added "rm -f $$d/qemu-options.def" to the for d in
$(ALL_SUBDIRS) loop.  That file doesn't exist.  Remove the mistaken
rm.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190528082308.22032-3-armbru@redhat.com>

Makefile

@@ -678,7 +678,6 @@ clean:
 	rm -rf qga/qapi-generated
 	for d in $(ALL_SUBDIRS); do \
 	if test -d $$d; then $(MAKE) -C $$d $@ || exit 1; fi; \
-	rm -f $$d/qemu-options.def; \
         done
 	rm -f config-all-devices.mak