remove duplicate exception close tag

Co-authored-by: Genevieve Warren <[email protected]>

Author: trivalik

xml/System.Windows/Clipboard.xml

@@ -874,7 +874,7 @@
         </remarks>
         <exception cref="T:System.Runtime.InteropServices.ExternalException">The Clipboard could not be cleared. This typically occurs when the Clipboard is being used by another process.</exception>
         <exception cref="T:System.ArgumentNullException">
-          <paramref name="format" /> is <see langword="String.Empty" />.</exception>
+          <paramref name="format" /> is <see langword="String.Empty" />.
 
 -or-