Remove some unused members

ICSharpCode.Decompiler/CSharp/Syntax/Expressions/ArrayInitializerExpression.cs

@@ -34,18 +34,6 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 	[DecompilerAstNode(hasNullNode: true, hasPatternPlaceholder: true)]
 	public partial class ArrayInitializerExpression : Expression
 	{
-		/// <summary>
-		/// For ease of use purposes in the resolver the ast representation
-		/// of { a, b, c }  is { {a}, {b}, {c} }.
-		/// If IsSingleElement is true then this array initializer expression is a generated one.
-		/// That has no meaning in the source code (and contains no brace tokens).
-		/// </summary>
-		public virtual bool IsSingleElement {
-			get {
-				return false;
-			}
-		}
-
 		public ArrayInitializerExpression()
 		{
 		}
@@ -77,23 +65,6 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			ArrayInitializerExpression o = other as ArrayInitializerExpression;
 			return o != null && this.Elements.DoMatch(o.Elements, match);
 		}
-
-		public static ArrayInitializerExpression CreateSingleElementInitializer()
-		{
-			return new SingleArrayInitializerExpression();
-		}
-		/// <summary>
-		/// Single elements in array initializers are represented with this special class.
-		/// </summary>
-		class SingleArrayInitializerExpression : ArrayInitializerExpression
-		{
-			public override bool IsSingleElement {
-				get {
-					return true;
-				}
-			}
-
-		}
 	}
 }
 

ICSharpCode.Decompiler/CSharp/Syntax/Role.cs

@@ -88,15 +88,6 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			return node is T;
 		}
 
-		[Obsolete("Use the other overload explicitly specifying the nullObject.")]
-		public Role(string name)
-		{
-			if (name == null)
-				throw new ArgumentNullException(nameof(name));
-			this.name = name;
-			this.nullObject = null!;
-		}
-
 		public Role(string name, T nullObject)
 		{
 			this.name = name ?? throw new ArgumentNullException(nameof(name));

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/EntityDeclaration.cs

@@ -16,6 +16,7 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 
@@ -33,6 +34,7 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			get { return NodeType.Member; }
 		}
 
+		[Obsolete]
 		public abstract SymbolKind SymbolKind { get; }
 
 		public AstNodeCollection<AttributeSection> Attributes {