iwlwifi: remove duplicate rate scale init code

The rate scale windows are cleared twice as part of the init.
Cleanup this duplication in both mvm and dvm.

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>