XEP-0198: Remove leftover optional and required children in sm element (#1447)

Both had been removed from the example in
0dcc653, and were only specified in the
XML Schema in 0.10 (see 44d5857).

They were never specified.

Author: linkmauve

xep-0198.xml

@@ -30,6 +30,12 @@
   &dcridland;
   &mwild;
   &tmolitor;
+  <revision>
+    <version>1.6.3</version>
+    <date>2025-07-28</date>
+    <initials>egp</initials>
+    <remark><p>Remove leftover &lt;optional/&gt; and &lt;required/&gt; children in &lt;sm/&gt; element.</p></remark>
+  </revision>
   <revision>
     <version>1.6.2</version>
     <date>2024-09-24</date>
@@ -769,14 +775,7 @@
 
   <xs:element name='resumed' type='resumptionElementType'/>
 
-  <xs:element name='sm'>
-    <xs:complexType>
-      <xs:choice>
-        <xs:element name='optional' type='empty'/>
-        <xs:element name='required' type='empty'/>
-      </xs:choice>
-    </xs:complexType>
-  </xs:element>
+  <xs:element name='sm' type='empty'/>
 
   <xs:complexType name='resumptionElementType'>
     <xs:simpleContent>