nspawn: don't provide /dev/rtc0 in the container

Since RTCs are hardware devices and are very much shared resources we
should avoid to provide them in each container.

src/nspawn/nspawn.c

@@ -443,8 +443,7 @@ static int copy_devnodes(const char *dest) {
                 "random\0"
                 "urandom\0"
                 "tty\0"
-                "ptmx\0"
+                "ptmx\0";
-                "rtc0\0";
 
         const char *d;
         int r = 0;