Fix summary of Binding.PropertyName (#2356)

Author: hughbe

xml/System.Windows.Forms/Binding.xml

@@ -1352,7 +1352,7 @@
         <ReturnType>System.String</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Gets or sets the name of the control's data-bound property.</summary>
+        <summary>Gets the name of the control's data-bound property.</summary>
         <value>The name of a control property to bind to.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[