slapos_cloud: destination_reference isn't required if the document is destroyed

master/bt5/slapos_cloud/PropertySheetTemplateItem/portal_property_sheets/SoftwareInstanceConstraint/not_destroy_requested_property_existence_constraint.xml

@@ -24,6 +24,7 @@
               <tuple>
                 <string>ssl_certificate</string>
                 <string>ssl_key</string>
+                <string>destination_reference</string>
               </tuple>
             </value>
         </item>

master/bt5/slapos_cloud/PropertySheetTemplateItem/portal_property_sheets/SoftwareInstanceConstraint/property_existence_constraint.xml

@@ -22,7 +22,6 @@
             <key> <string>constraint_property</string> </key>
             <value>
               <tuple>
-                <string>destination_reference</string>
                 <string>reference</string>
               </tuple>
             </value>