src/basic: rename audit.[ch] → audit-util.[ch] and capability.[ch] → capability-util.[ch]

The files are named too generically, so that they might conflict with
the upstream project headers. Hence, let's add a "-util" suffix, to
clarify that this are just our utility headers and not any official
upstream headers.

src/core/execute.c

@@ -60,7 +60,7 @@
 #include "barrier.h"
 #include "bus-endpoint.h"
 #include "cap-list.h"
-#include "capability.h"
+#include "capability-util.h"
 #include "def.h"
 #include "env-util.h"
 #include "errno-list.h"