Delete unused linkedhashqueue.cs

src/Workspaces/Core/Portable/Utilities/CompilerUtilities/linkedhashqueue.cs

-// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
-
-using System;
-using System.Collections;
-using System.Collections.Generic;
-
-namespace Roslyn.Utilities
-{
-    /// <summary>
-    /// A queue that will only allow one instance of an object inside of it at a time.  When an
-    /// object is enqueued that is already in the list, it is removed from its location and placed
-    /// at the end of the queue.  These aspects make the queue useful for LRU caches.
-    /// 
-    /// This class is not thread-safe.  If you need it to be, wrap it within your own lock.
-    /// </summary>
-    internal class LinkedHashQueue<T> : IEnumerable<T>
-    {
-        private readonly LinkedList<T> _list;
-        private readonly Dictionary<T, LinkedListNode<T>> _map;
-        private int _insertionIndex;
-
-        public LinkedHashQueue()
-            : this(null)
-        {
-        }
-
-        public LinkedHashQueue(IEqualityComparer<T> comparer)
-        {
-            _list = new LinkedList<T>();
-            _map = new Dictionary<T, LinkedListNode<T>>(comparer);
-        }
-
-        public int Count => _list.Count;
-
-        public void Clear()
-        {
-            _list.Clear();
-            _map.Clear();
-            _insertionIndex = 0;
-        }
-
-        public T First => _list.First.Value;
-
-        /// <summary>
-        /// Adds this item (or moves it if it's already in the queue) to the end.  If the item is not
-        /// in the list, 'true' is returned, otherwise 'false'.
-        /// </summary>
-        public bool Enqueue(T value)
-        {
-            var result = true;
-            if (_map.TryGetValue(value, out var node))
-            {
-                // Already had this in the list.  Return 'false'.  
-                result = false;
-                _list.Remove(node);
-            }
-
-            node = _list.AddLast(value);
-            _insertionIndex++;
-            _map[value] = node;
-
-            return result;
-        }
-
-        public T Dequeue()
-        {
-            if (this.Count == 0)
-            {
-                throw new InvalidOperationException();
-            }
-
-            var node = _list.First;
-            _list.RemoveFirst();
-            _map.Remove(node.Value);
-
-            return node.Value;
-        }
-
-        public bool Contains(T value)
-        {
-            return _map.TryGetValue(value, out var node);
-        }
-
-        public void Remove(T value)
-        {
-            _map.TryGetValue(value, out var node);
-            if (_map.Remove(value))
-            {
-                _list.Remove(node);
-            }
-        }
-
-        public IEnumerator<T> GetEnumerator()
-        {
-            return _list.GetEnumerator();
-        }
-
-        IEnumerator IEnumerable.GetEnumerator()
-        {
-            return GetEnumerator();
-        }
-    }
-}