plugin list: delete implementation:

`delete` is similar to XEP-0060's retractItem, but node is set to default ticket one if
not specified.

sat/plugins/plugin_misc_lists.py

@@ -248,6 +248,14 @@ class PubsubLists:
             method=self._set,
             async_=True,
         )
+        host.bridge.addMethod(
+            "listDeleteItem",
+            ".plugin",
+            in_sign="sssbs",
+            out_sign="",
+            method=self._delete,
+            async_=True,
+        )
         host.bridge.addMethod(
             "listSchemaGet",
             ".plugin",
@@ -340,7 +348,7 @@ class PubsubLists:
                 - 'updated' is set everytime
         @param extra(dict, None): same as for [XEP-0060.sendItem] with additional keys:
             - update(bool): if True, get previous item data to merge with current one
-                if True, item_id must be None
+                if True, item_id must be set
         other arguments are same as for [self._s.sendDataFormItem]
         @return (unicode): id of the created item
         """
@@ -376,6 +384,32 @@ class PubsubLists:
             client, service, node, values, schema, item_id, extra, deserialise, form_ns
         )
 
+    def _delete(
+        self, service_s, nodeIdentifier, itemIdentifier, notify, profile_key
+    ):
+        client = self.host.getClient(profile_key)
+        return defer.ensureDeferred(self.delete(
+            client,
+            jid.JID(service_s) if service_s else None,
+            nodeIdentifier,
+            itemIdentifier,
+            notify
+        ))
+
+    async def delete(
+        self,
+        client: SatXMPPEntity,
+        service: Optional[jid.JID],
+        node: Optional[str],
+        itemIdentifier: str,
+        notify: Optional[bool] = None
+    ) -> None:
+        if not node:
+            node = self.namespace
+        return await self._p.retractItems(
+            service, node, (itemIdentifier,), notify, client.profile
+        )
+
     def _listsList(self, service, node, profile):
         service = jid.JID(service) if service else None
         node = node or None