[mac] Fix enabled on TabButton

Was a change trying to get the disabled look, got left in when submitting.

Author: Eric Maupin

Xamarin.PropertyEditing.Mac/Controls/Custom/TabButton.cs

@@ -34,7 +34,6 @@ public bool Selected
 			get { return this.selected; }
 			set
 			{
-				Enabled = value;
 				this.selected = value;
 				NeedsDisplay = true;
 			}