Remove unused "hasTransactionManager" method

Closes gh-7592

spring-boot/src/main/java/org/springframework/boot/orm/jpa/hibernate/SpringJtaPlatform.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2014 the original author or authors.
+ * Copyright 2012-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -44,10 +44,6 @@ public class SpringJtaPlatform extends AbstractJtaPlatform {
 		this.transactionManager = transactionManager;
 	}
 
-	protected boolean hasTransactionManager() {
-		return true;
-	}
-
 	@Override
 	protected TransactionManager locateTransactionManager() {
 		return this.transactionManager.getTransactionManager();