If timestamp is not listed in sp, don't sign

Author: blaggacao

src/zeep/wsse/signature.py

@@ -247,12 +247,7 @@ def _signature_prepare(envelope, key, signature_method, digest_method, signature
     # Perform the actual signing.
     ctx = xmlsec.SignatureContext()
     ctx.key = key
-    # Sign default elements if present
-    timestamp = security.find(QName(ns.WSU, "Timestamp"))
-    if timestamp != None:
-        _sign_node(ctx, signature, timestamp, digest_method)
-
-    # Sign extra elements defined in WSDL
+    # Sign elements defined in WSDL
     if signatures is not None:
         if signatures["body"] or signatures["everything"]:
             _sign_node(