remove DocumentName

src/Features/Core/Portable/FindUsages/ExternalReferenceItem.cs

@@ -19,18 +19,15 @@ internal abstract class ExternalReferenceItem
         public ExternalReferenceItem(
             DefinitionItem definition,
             string documentName,
-            string projectName,
             object text,
             string displayPath)
         {
             Definition = definition;
             DocumentName = documentName;
-            ProjectName = projectName;
             Text = text;
             DisplayPath = displayPath;
         }
 
-        public string DocumentName { get; }
         public string ProjectName { get; }
         /// <remarks>
         /// Must be of type Microsoft.VisualStudio.Text.Adornments.ImageElement or