iwlwifi: mvm: remove traffic load monitoring in rs

The traffic load monitoring isn't used anymore to decide whether
a Tx aggregation on a specific TID should be started.
No point in collecting these statistics. Remove the relevant code.

Signed-off-by: Eyal Shapira <eyal@wizery.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>