Enable the <assert.h>-checking test; fix violations.

* Makefile.cfg (local-checks-to-skip)
[sc_prohibit_assert_without_use]: Enable.
* qemud/mdns.c: Don't include <assert.h>; no uses of assert here.
* qemud/qemud.c: Likewise.
* qemud/remote.c: Likewise.

qemud/remote.c

@@ -43,7 +43,6 @@
 #include <errno.h>
 #include <getopt.h>
 #include <ctype.h>
-#include <assert.h>
 #include <fnmatch.h>
 
 #ifdef HAVE_POLKIT