Remove “dry_run” from opcodes.OpCreateInstance

I'ts declared twice, once in opcodes.OpCode and here, and this one
is redundant.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

lib/opcodes.py

@@ -480,7 +480,6 @@ class OpCreateInstance(OpCode):
     "source_handshake",
     "source_x509_ca",
     "source_instance_name",
-    "dry_run",
     ]