wifi: mt76: mt7915: remove VHT160 capability on MT7915

The IEEE80211_VHT_CAP_EXT_NSS_BW value already indicates support for half-NSS
160 MHz support, so it is wrong to also advertise full 160 MHz support.

Fixes: c2f73eac ("wifi: mt76: mt7915: add back 160MHz channel width support for MT7915")
Signed-off-by: Felix Fietkau <nbd@nbd.name>