Remove not needed invocation and null forgiving operators

Author: nicolaihenriksen

src/MaterialDesignThemes.Wpf/Behaviors/TextBoxHorizontalScrollBarBehavior.cs

@@ -46,8 +46,6 @@ private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
     {
         AssociatedObject.HorizontalScrollBarVisibility = ScrollBarVisibility.Hidden;
         _builtInScrollBar = AssociatedObject.FindChild<ScrollBar>("PART_HorizontalScrollBar");
-
-        AssociatedObject_SizeChanged(sender, null!);    // TODO: Possibly not needed
     }
 
     private void AssociatedObject_SizeChanged(object sender, SizeChangedEventArgs e)
@@ -56,7 +54,7 @@ private void AssociatedObject_SizeChanged(object sender, SizeChangedEventArgs e)
 
         ts.ViewportSize = AssociatedObject.ViewportWidth;
         ts.Value = AssociatedObject.HorizontalOffset;
-        ts.Maximum = _builtInScrollBar!.Maximum;
+        ts.Maximum = _builtInScrollBar.Maximum;
         UpdateTargetScrollBarVisibility(_builtInScrollBar!.Maximum > 0);
     }
 
@@ -65,7 +63,7 @@ private void AssociatedObject_ScrollChanged(object sender, ScrollChangedEventArg
         if (TargetScrollBar is not { } ts || _builtInScrollBar is null) return;
 
         ts.Value = AssociatedObject.HorizontalOffset;
-        ts.Maximum = _builtInScrollBar!.Maximum;
+        ts.Maximum = _builtInScrollBar.Maximum;
         UpdateTargetScrollBarVisibility(_builtInScrollBar!.Maximum > 0);
     }