Remove deprecated SynthesizedAnnotation interface

The SynthesizedAnnotation interface is no longer used in the core
Spring Framework and should not be used by external parties either.

Closes gh-29092

spring-core/src/main/java/org/springframework/core/annotation/SynthesizedAnnotation.java

@@ -1,32 +0,0 @@
-/*
- * Copyright 2002-2022 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.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.springframework.core.annotation;
-
-/**
- * Marker interface implemented by synthesized annotation proxies.
- *
- * <p>Used to detect whether an annotation has already been synthesized.
- *
- * @author Sam Brannen
- * @since 4.2
- * @deprecated For removal prior to Spring Framework 6.0; use
- * {@link AnnotationUtils#isSynthesizedAnnotation(java.lang.annotation.Annotation)}
- * instead.
- */
-@Deprecated
-public interface SynthesizedAnnotation {
-}