There is no benefit in retaining the legacy rate control module
in the driver codebase.

It is known to be buggy and has less than optimal performance
in real-world environments compared with minstrel. The only
reason that it was kept when we made the switch to minstrel
as default was that it showed higher throughput numbers in a
clean/ideal environment.

This is no longer the case and minstrel can push ath9k to
the same throughput levels. In TCP, with 3-stream cards, more than
295 Mbps can be obtained in open air, with 2-stream cards,
210 Mbps is easily reached. To test performance issues,
instead of using a broken rate control module, it is better
to use the fixed-rate interface provided by mac80211 anyway.

The ath9k RC has not received any bug fixes in years and is
just bit-rotting away - this patch removes it.
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>