Remove our own impl of ReadOnlyList and update usages

OpenRA.Game/Primitives/ReadOnlyList.cs

@@ -1,81 +0,0 @@
-#region Copyright & License Information
-/*
- * Copyright 2007-2020 The OpenRA Developers (see AUTHORS)
- * This file is part of OpenRA, which is free software. It is made
- * available to you under the terms of the GNU General Public License
- * as published by the Free Software Foundation, either version 3 of
- * the License, or (at your option) any later version. For more
- * information, see COPYING.
- */
-#endregion
-
-using System;
-using System.Collections.Generic;
-
-namespace OpenRA
-{
-	/// <summary>
-	/// A minimal read only list interface for .NET 4
-	/// </summary>
-	/// <remarks>
-	/// .NET 4.5 has an implementation built-in, this code is not meant to
-	/// duplicate it but provide a compatible interface that can be replaced
-	/// when we switch to .NET 4.5 or higher.
-	/// </remarks>
-	public interface IReadOnlyList<out T> : IEnumerable<T>
-	{
-		int Count { get; }
-		T this[int index] { get; }
-	}
-
-	public static class ReadOnlyList
-	{
-		public static IReadOnlyList<T> AsReadOnly<T>(this IList<T> list)
-		{
-			return list as IReadOnlyList<T> ?? new ReadOnlyList<T>(list);
-		}
-	}
-
-	/// <summary>
-	/// A minimal read only list for .NET 4 implemented as a wrapper
-	/// around an IList.
-	/// </summary>
-	public class ReadOnlyList<T> : IReadOnlyList<T>
-	{
-		private readonly IList<T> list;
-
-		public ReadOnlyList()
-			: this(new List<T>())
-		{
-		}
-
-		public ReadOnlyList(IList<T> list)
-		{
-			if (list == null)
-				throw new ArgumentNullException(nameof(list));
-
-			this.list = list;
-		}
-
-		#region IEnumerable implementation
-		public IEnumerator<T> GetEnumerator()
-		{
-			return list.GetEnumerator();
-		}
-		#endregion
-
-		#region IEnumerable implementation
-		System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
-		{
-			return list.GetEnumerator();
-		}
-		#endregion
-
-		#region IReadOnlyList implementation
-		public int Count => list.Count;
-
-		public T this[int index] => list[index];
-
-		#endregion
-	}
-}