iwlwifi: mvm: remove buggy and unnecessary hw_queue initialization

After converting the driver to TXQs, it no longer has any reason
to initialize vif->hw_queue/vif->cab_queue since it no longer sets
the HW_QUEUE_CONTROL flag. Remove the code that initialized those,
it was broken due to relying on an uninitialized stack value in
used_hw_queues, as Colin reported.

Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>