core: more exact test on the procfs special string "(deleted)"

In other parts of systemd, the code checks for " (deleted)",
but in one instance, it did not (yet). Make it do the same.

(cherry picked from commit a87f0f726c)

src/core/umount.c

@@ -170,7 +170,7 @@ static int swap_list_get(MountPoint **head) {
                         continue;
                 }
 
-                if (endswith(dev, "(deleted)")) {
+                if (endswith(dev, " (deleted)")) {
                         free(dev);
                         continue;
                 }