Elements. Remove FormalParameterElementImpl.reference

Formal parameters cannot be referenced non-locally, so we never set
references for them.

Change-Id: I7b6b3437f029b7e04bb1f0c4dbdb893286e1db1d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/442166
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/element/element.dart

@@ -3094,8 +3094,6 @@ class FieldFragmentImpl extends PropertyInducingFragmentImpl
 
 class FormalParameterElementImpl extends PromotableElementImpl
     with FormalParameterElementMixin {
-  @override
-  Reference? reference;
   final FormalParameterFragmentImpl wrappedElement;
 
   @override