ath10k: remove VHT capabilities from 2.4GHz

According to the spec, VHT doesn't exist in 2.4GHz.

There are vendor extensions to allow a subset of VHT to work
(notably 256-QAM), but since mac80211 doesn't support those
advertising VHT capability on 2.4GHz leads to the behaviour
of reporting VHT capabilities but not being able to use any
of them due to mac80211's code requiring 80 MHz support.

Remove the VHT capabilities from 2.4GHz for now. If mac80211
gets extended to use the (likely Broadcom) vendor IEs for it
and handles the lack of 80 MHz support, it can be added back.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>