wifi: iwlwifi: mvm: Remove unused last_sub_index from reorder buffer

The last_sub_index field is not used and appears to be a leftover
from a previous implementation, remove it.

Signed-off-by: Daniel Gabay <daniel.gabay@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20240901071542.da75cfef9144.I6e1fb635b2893618e6bd28501fb858042d8aa44e@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>