Clarify some ObjectStateFormatter APIs are no-ops (#4256)

Author: GrabYourPitchforks

xml/System.Web.UI/ObjectStateFormatter.xml

@@ -324,6 +324,8 @@
           <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
+ Setting this property has no effect.
+  
  This member is an explicit interface member implementation. It can be used only when the <xref:System.Web.UI.ObjectStateFormatter> instance is cast to an <xref:System.Runtime.Serialization.IFormatter> interface.  
   
  ]]></format>
@@ -356,6 +358,8 @@
           <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
+ Setting this property has no effect.
+  
  This member is an explicit interface member implementation. It can be used only when the <xref:System.Web.UI.ObjectStateFormatter> instance is cast to an <xref:System.Runtime.Serialization.IFormatter> interface.  
   
  ]]></format>
@@ -471,6 +475,8 @@
           <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
+ Setting this property has no effect.
+  
  This member is an explicit interface member implementation. It can be used only when the <xref:System.Web.UI.ObjectStateFormatter> instance is cast to an <xref:System.Runtime.Serialization.IFormatter> interface.  
   
  ]]></format>