generate_packets.py: remove Variant members only needed on Packets
Reply To alienvalkyrie
or that can be taken unmodified from the packet this is a variant of.
This patch leaves some of those fields in if they are used in a lot of places – those should be turned into properties in #44768.
Part of #43927. Some code is unnecessarily duplicated between Packets and Variants. Remove the fields and members of the Variant class that are only used on Packets, or that can be taken unmodified from the packet this is a variant of.