Remove unnecessary variable declaration in ProxyCallbackFilter

Closes gh-24675

spring-aop/src/main/java/org/springframework/aop/framework/CglibAopProxy.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -876,15 +876,14 @@ class CglibAopProxy implements AopProxy, Serializable {
 					}
 					return AOP_PROXY;
 				}
-				Method key = method;
 				// Check to see if we have fixed interceptor to serve this method.
 				// Else use the AOP_PROXY.
-				if (isStatic && isFrozen && this.fixedInterceptorMap.containsKey(key)) {
+				if (isStatic && isFrozen && this.fixedInterceptorMap.containsKey(method)) {
 					if (logger.isTraceEnabled()) {
 						logger.trace("Method has advice and optimizations are enabled: " + method);
 					}
 					// We know that we are optimizing so we can use the FixedStaticChainInterceptors.
-					int index = this.fixedInterceptorMap.get(key);
+					int index = this.fixedInterceptorMap.get(method);
 					return (index + this.fixedInterceptorOffset);
 				}
 				else {