Delete AnnotationAttributeExtractor

Delete `AnnotationAttributeExtractor` which is package private and
no longer used.

Closes gh-22753

Author: philwebb

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

@@ -41,7 +41,6 @@
  * @since 5.2
  * @param <A> the annotation type
  * @see Annotation
- * @see AnnotationAttributeExtractor
  * @see AnnotationUtils#synthesizeAnnotation(Annotation, AnnotatedElement)
  */
 final class SynthesizedMergedAnnotationInvocationHandler<A extends Annotation> implements InvocationHandler {