EStructuralFeatureValueProviderBase/DerivedAnnotationValueProviderBase: Remove support to implement multiple annotations with one EClass

EStructuralFeatureValueProviderBase/DerivedAnnotationValueProviderBase provide constructors to select an EAttribute / an EReference to back an annotation. The feature is currently not used (i.e., all annotations are implemented by dedicated EClasses), and the new JavaFX-based editors does not support to show more than one annotation stemming from a given class.

Therefore, the two aforementioned constructors should be removed to avoid misuse of the API.