Remove unnecessary empty array static fields

As I was touching Stack, I noticed that it and Queue had an empty array static field, which was just being initialized to Array.Empty(). The field is unnecessary, and the call site can just use Array.Empty directly.  This commit just cleans that up and some unnecessary field setting in the ctors.

Author: stephentoub

src/System.Collections/src/System/Collections/Generic/Queue.cs

@@ -32,14 +32,13 @@ public class Queue<T> : IEnumerable<T>,
         private const int MinimumGrow = 4;
         private const int GrowFactor = 200;  // double each time
         private const int DefaultCapacity = 4;
-        private static T[] s_emptyArray = Array.Empty<T>();
 
         // Creates a queue with room for capacity objects. The default initial
         // capacity and grow factor are used.
         /// <include file='doc\Queue.uex' path='docs/doc[@for="Queue.Queue"]/*' />
         public Queue()
         {
-            _array = s_emptyArray;
+            _array = Array.Empty<T>();
         }
 
         // Creates a queue with room for capacity objects. The default grow factor
@@ -50,11 +49,7 @@ public Queue(int capacity)
         {
             if (capacity < 0)
                 throw new ArgumentOutOfRangeException("capacity", SR.ArgumentOutOfRange_NeedNonNegNumRequired);
-
             _array = new T[capacity];
-            _head = 0;
-            _tail = 0;
-            _size = 0;
         }
 
         // Fills a Queue with the elements of an ICollection.  Uses the enumerator
@@ -67,8 +62,6 @@ public Queue(IEnumerable<T> collection)
                 throw new ArgumentNullException("collection");
 
             _array = new T[DefaultCapacity];
-            _size = 0;
-            _version = 0;
 
             using (IEnumerator<T> en = collection.GetEnumerator())
             {

src/System.Collections/src/System/Collections/Generic/Stack.cs

@@ -29,14 +29,11 @@ public class Stack<T> : IEnumerable<T>,
         private Object _syncRoot;
 
         private const int DefaultCapacity = 4;
-        private static T[] s_emptyArray = Array.Empty<T>();
 
         /// <include file='doc\Stack.uex' path='docs/doc[@for="Stack.Stack"]/*' />
         public Stack()
         {
-            _array = s_emptyArray;
-            _size = 0;
-            _version = 0;
+            _array = Array.Empty<T>();
         }
 
         // Create a stack with a specific initial capacity.  The initial capacity
@@ -47,8 +44,6 @@ public Stack(int capacity)
             if (capacity < 0)
                 throw new ArgumentOutOfRangeException("capacity", SR.ArgumentOutOfRange_NeedNonNegNumRequired);
             _array = new T[capacity];
-            _size = 0;
-            _version = 0;
         }
 
         // Fills a Stack with the contents of a particular collection.  The items are
@@ -59,7 +54,6 @@ public Stack(IEnumerable<T> collection)
         {
             if (collection == null)
                 throw new ArgumentNullException("collection");
-
             _array = EnumerableHelpers.ToArray(collection, out _size);
         }