mac80211: minstrel_ht: remove old ewma based rate average code

The new noise filter has been the default for a while now with no reported
downside and significant improvement compared to the old code.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20210115120242.89616-5-nbd@nbd.name


Signed-off-by: Johannes Berg <johannes.berg@intel.com>