8320786: Remove ThreadGroup.stop

Reviewed-by: rriggs, dholmes, jpai

src/java.base/share/classes/java/lang/ThreadGroup.java

@@ -554,17 +554,6 @@ public class ThreadGroup implements Thread.UncaughtExceptionHandler {
         return i;
     }
 
-    /**
-     * Throws {@code UnsupportedOperationException}.
-     *
-     * @deprecated This method was originally specified to stop all threads in
-     *             the thread group. It was inherently unsafe.
-     */
-    @Deprecated(since="1.2", forRemoval=true)
-    public final void stop() {
-        throw new UnsupportedOperationException();
-    }
-
     /**
      * Interrupts all {@linkplain Thread#isAlive() live} platform threads in
      * this thread group and its subgroups.

test/jdk/java/lang/ThreadGroup/BasicTests.java

@@ -732,12 +732,6 @@ class BasicTests {
         group.list();
     }
 
-    @Test
-    void testStop() {
-        ThreadGroup group = new ThreadGroup("foo");
-        assertThrows(UnsupportedOperationException.class, () -> group.stop());
-    }
-
     @Test
     void testNull1() {
         assertThrows(NullPointerException.class,