Remove old Unused ProgressRing from ImageEx control

Fixes #3741

Author: michael-hawker

Microsoft.Toolkit.Uwp.UI.Controls.Core/ImageEx/ImageExBase.cs

@@ -21,7 +21,6 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     [TemplateVisualState(Name = UnloadedState, GroupName = CommonGroup)]
     [TemplateVisualState(Name = FailedState, GroupName = CommonGroup)]
     [TemplatePart(Name = PartImage, Type = typeof(object))]
-    [TemplatePart(Name = PartProgress, Type = typeof(ProgressRing))]
     public abstract partial class ImageExBase : Control
     {
         private bool _isInViewport;
@@ -31,11 +30,6 @@ public abstract partial class ImageExBase : Control
         /// </summary>
         protected const string PartImage = "Image";
 
-        /// <summary>
-        /// ProgressRing name in template
-        /// </summary>
-        protected const string PartProgress = "Progress";
-
         /// <summary>
         /// VisualStates name in template
         /// </summary>
@@ -66,11 +60,6 @@ public abstract partial class ImageExBase : Control
         /// </summary>
         protected object Image { get; private set; }
 
-        /// <summary>
-        /// Gets backing object for the ProgressRing
-        /// </summary>
-        protected ProgressRing Progress { get; private set; }
-
         /// <summary>
         /// Gets object used for lock
         /// </summary>
@@ -169,7 +158,6 @@ protected override void OnApplyTemplate()
             RemoveImageFailed(OnImageFailed);
 
             Image = GetTemplateChild(PartImage) as object;
-            Progress = GetTemplateChild(PartProgress) as ProgressRing;
 
             IsInitialized = true;