Update ns-System.Net.Mail.xml (#2420)

* Update ns-System.Net.Mail.xml

Lift the warning from SmtpClient to the namespace to make it clearer this is now obsolete.

* Update ns-System.Net.Mail.xml

Author: stephenegriffin

xml/ns-System.Net.Mail.xml

@@ -5,8 +5,8 @@
       <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
- The <xref:System.Net.Mail.MailMessage> class represents the content of a mail message. The <xref:System.Net.Mail.SmtpClient> class transmits email to the SMTP host that you designate for mail delivery. You can create mail attachments using the <xref:System.Net.Mail.Attachment> class.  
-  
+The <xref:System.Net.Mail.MailMessage> class represents the content of a mail message. You can create mail attachments using the <xref:System.Net.Mail.Attachment> class.  
+
  ]]></format>
     </remarks>
     <altmember cref="N:System.Net" />
@@ -20,4 +20,4 @@
     <related type="Article" href="~/docs/framework/network-programming/network-tracing.md">Network Tracing in the .NET Framework</related>
     <related type="Article" href="~/docs/framework/network-programming/security-in-network-programming.md">Security in Network Programming</related>
   </Docs>
-</Namespace>
+</Namespace>