Updating Associated Metadata Provider to follow the existing pattern.

cc @dougbu @rynowak 
hmm, this is an odd case.  we don't have other properties with different defaults in `ModelMetadata` and `CachedDataAnnotationsModelMetadata`.  that isn't something we should introduce unless absolutely necessary.  even then, deserves discussion.

is it possible to fall through to calling `base.ComputeBinderIncludeProperties()` without changing everything else in this PR?  realize a consumer or two must change.  but is the update large?