wifi: iwlwifi: mvm: remove new checksum code

The hardware isn't going to get fixed, so this mode cannot work
in the foreseeable future. Remove it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230614145722.ddbc16c4affe.Ia6921e4b8a9624d4f57489ac775105ed0e400313@changeid


[restore original subject]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>