iwlwifi: mvm: remove txq EMPTYING_DELBA state for DQA

In DQA mode, there is no need to wait for the TXQ to
clear out after getting a DELBA, since traffic can
continue running on the queue.

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>