Address PR feedback

Author: stephentoub

src/System.Private.CoreLib/src/System/Threading/CancellationTokenSource.cs

@@ -205,7 +205,7 @@ public CancellationTokenSource(int millisecondsDelay)
         private void InitializeWithTimer(int millisecondsDelay)
         {
             _state = NotCanceledState;
-            _timer = Timer.UnsafeCreate(s_timerCallback, this, millisecondsDelay, -1);
+            _timer = new Timer(s_timerCallback, this, millisecondsDelay, -1, flowExecutionContext: false);
         }
 
         /// <summary>Communicates a request for cancellation.</summary>
@@ -345,7 +345,7 @@ public void CancelAfter(int millisecondsDelay)
                 // Initially set to "never go off" because we don't want to take a
                 // chance on a timer "losing" the initialization and then
                 // cancelling the token before it (the timer) can be disposed.
-                Timer newTimer = Timer.UnsafeCreate(s_timerCallback, this, -1, -1);
+                Timer newTimer = new Timer(s_timerCallback, this, -1, -1, flowExecutionContext: false);
                 if (Interlocked.CompareExchange(ref _timer, newTimer, null) != null)
                 {
                     // We did not initialize the timer.  Dispose the new timer.

src/System.Private.CoreLib/src/System/Threading/Timer.cs

@@ -685,11 +685,11 @@ public Timer(TimerCallback callback,
         {
         }
 
-        private Timer(TimerCallback callback,
-                      object state,
-                      int dueTime,
-                      int period,
-                      bool flowExecutionContext)
+        internal Timer(TimerCallback callback,
+                       object state,
+                       int dueTime,
+                       int period,
+                       bool flowExecutionContext)
         {
             if (dueTime < -1)
                 throw new ArgumentOutOfRangeException(nameof(dueTime), SR.ArgumentOutOfRange_NeedNonNegOrNegative1);
@@ -699,10 +699,6 @@ private Timer(TimerCallback callback,
             TimerSetup(callback, state, (uint)dueTime, (uint)period, flowExecutionContext);
         }
 
-        // TODO https://github.com/dotnet/corefx/issues/26523: Consider making public.
-        internal static Timer UnsafeCreate(TimerCallback callback, object state, int dueTime, int period) =>
-            new Timer(callback, state, dueTime, period, flowExecutionContext: false);
-
         public Timer(TimerCallback callback,
                      object state,
                      TimeSpan dueTime,