minstrel_ht: Remove unused function parameters

Remove unused function parameters in the following functions:
minstrel_calc_rate_ewma()
minstrel_ht_calc_tp()
minstrel_aggr_check()
minstrel_ht_set_rate()

Signed-off-by: Patrick Kelle <patrick.kelle81@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>