Unit test: remove printf again, since they do not help

Travis CI fails with "(after this point) Test timeout expired"
The idea was to print something to stdout every some seconds,
but this does not help. Thus, the printf lines are removed again.

test/public_server.c

@@ -74,14 +74,14 @@ static int wait_not_null(void *volatile *data)
 {
 	int i;
 	for (i = 0; i < 100; i++) {
-        printf("Waiting for response ... %i\n", i);
+        /* printf("Waiting for response ... %i\n", i); */s
 		test_sleep(1);
 		if (*data != NULL) {
-            printf("Waiting for response ... %i (done)\n", i);
+            /* printf("Waiting for response ... %i (done)\n", i); */
 			return 1;
 		}
 	}
-    printf("Waiting for response ... %i (failed)\n", i);
+    /* printf("Waiting for response ... %i (failed)\n", i); */
 	return 0;
 }