iwlwifi: remove max_ht_ampdu_exponent config parameter

commit edba17ad

 upstream.

This always has the same value, since we don't have any
devices with different values; remove the parameter.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210210171218.50d11cbb073f.Ia44d022a4c549eb5fe0254fb20c62aa8d0bba634@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>