tmpfiles: remove spurious include of <sys/capability.h>

It does not use any functions from libcap directly. The CAP_MKNOD constant in
use by this file comes from <linux/capability.h> imported through "missing.h".

Tested that "systemd-tmpfiles" builds cleanly and works after this change.

src/tmpfiles/tmpfiles.c

@@ -38,7 +38,6 @@
 #include <sys/param.h>
 #include <glob.h>
 #include <fnmatch.h>
-#include <sys/capability.h>
 #include <sys/xattr.h>
 
 #include "log.h"