Drop AnnotationDefault attribute as unused.

Evidences:
1) Its constructor just swallowed an ElementValue without keeping it.
As such, this class has no getter methods and thus provides no value.

2) AnnotationDefault attribute is used to declare default value for an element (aka method) of an annotation.
As Tomcat is not interested in Annotation declarations, this attribute is of no interest.
Essentially, it scans for known annotations on classes. It is not interested in arbitrary other annotations.

Cobertura coverage report also showed no calls into AnnotationDefault class.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1624583 13f79535-47bb-0310-9956-ffa450edef68