Drop type_url_prefix from pack

Doesn't seem necessary.

Author: stefanvanburen

conformance/test/server.py

@@ -51,7 +51,7 @@
 # TODO: Use google.protobuf.any.pack on upgrade to protobuf==6.
 def pack(msg: "Message") -> Any:
     any_msg = Any()
-    any_msg.Pack(msg, type_url_prefix="'type.googleapis.com/'")
+    any_msg.Pack(msg)
     return any_msg