Update Application.xml (#4287)

Minor - minor change - removed the comma before "and" from Application.Deactivated Event description:
Occurs just before an application shuts down, and cannot be canceled.

Author: mdunka

xml/System.Windows/Application.xml

@@ -333,7 +333,7 @@
         <ReturnType>System.Windows.ExitEventHandler</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Occurs just before an application shuts down, and cannot be canceled.</summary>
+        <summary>Occurs just before an application shuts down and cannot be canceled.</summary>
         <remarks>
           <format type="text/markdown"><![CDATA[