Add support for removeOnCancelPolicy

This change removes the recently added SockJsThreadPoolTaskScheduler
and instead builds support for the removeOnCancelPolicy property in
ThreadPoolTaskScheduler and ScheduledExecutorFactoryBean.

Issue: SPR-11918

spring-websocket/src/test/java/org/springframework/web/socket/messaging/SubProtocolWebSocketHandlerTests.java

@@ -170,7 +170,7 @@ public class SubProtocolWebSocketHandlerTests {
 		assertTrue(session1.isOpen());
 		assertFalse(session2.isOpen());
 		assertNull(session1.getCloseStatus());
-		assertEquals(CloseStatus.PROTOCOL_ERROR, session2.getCloseStatus());
+		assertEquals(CloseStatus.SESSION_NOT_RELIABLE, session2.getCloseStatus());
 	}