Remove the now-unused IMemberReference interface

IdStringMemberReference was its only implementation and left with the
ID string grammar parser; unlike the NRefactory-era type system, IMember
does not extend IMemberReference here, so nothing in the library
produces or consumes it anymore.

Assisted-by: Claude:claude-fable-5:Claude Code

ICSharpCode.Decompiler/TypeSystem/IMember.cs

@@ -22,28 +22,6 @@ using System.Collections.Generic;
 
 namespace ICSharpCode.Decompiler.TypeSystem
 {
-	public interface IMemberReference
-	{
-		/// <summary>
-		/// Gets the declaring type reference for the member.
-		/// </summary>
-		ITypeReference DeclaringTypeReference { get; }
-
-		/// <summary>
-		/// Resolves the member.
-		/// </summary>
-		/// <param name="context">
-		/// Context to use for resolving this member reference.
-		/// Which kind of context is required depends on the which kind of member reference this is;
-		/// please consult the documentation of the method that was used to create this member reference,
-		/// or that of the class implementing this method.
-		/// </param>
-		/// <returns>
-		/// Returns the resolved member, or <c>null</c> if the member could not be found.
-		/// </returns>
-		IMember? Resolve(ITypeResolveContext context);
-	}
-
 	/// <summary>
 	/// Method/field/property/event.
 	/// </summary>

ICSharpCode.Decompiler/TypeSystem/TypeSystemExtensions.cs

@@ -485,8 +485,6 @@ namespace ICSharpCode.Decompiler.TypeSystem
 				return new ProjectedList<ITypeResolveContext, ITypeReference, IType>(context, typeReferences, (c, t) => t.Resolve(c));
 		}
 
-		// There is intentionally no Resolve() overload for IList<IMemberReference>: the resulting IList<Member> would
-		// contains nulls when there are resolve errors.
 		#endregion
 
 		#region IAssembly.GetTypeDefinition()