plugin XEP-0374: exluce openpgp element from XEP-0373 on send trigger:

the `openpgp` element is excluded to avoid useless double encryption.

rel 380

sat/plugins/plugin_xep_0374.py

@@ -382,6 +382,9 @@ class XEP_0374:
         # TODO: There should probably be explicitly forbidden elements here too, just as
         # for XEP-0420
         for child in list(stanza.elements()):
+            if child.name == "openpgp" and child.uri == NS_OX:
+                log.debug("not re-encrypting encrypted OX element")
+                continue
             # Remove the child from the stanza
             stanza.children.remove(child)