Remove the st_mtime check in vsm_refresh_set

Now that we incrementally read the file, the check if the mtime of the
index file has checked has to go away. If not, the index file will always
be marked as new, forcing a reread of the entire index.

lib/libvarnishapi/vsm.c

@@ -662,8 +662,7 @@ vsm_refresh_set(struct vsm *vd, struct vsm_set *vs)
 	    st.st_dev != vs->fst.st_dev ||
 	    st.st_mode != vs->fst.st_mode ||
 	    st.st_size < vs->fst.st_size ||
-	    st.st_nlink < 1 ||
-	    memcmp(&st.st_mtime, &vs->fst.st_mtime, sizeof st.st_mtime))) {
+	    st.st_nlink < 1)) {
 		closefd(&vs->fd);
 	}