ath6kl: Remove old 802.11a-only channels

Channels 34/38/42/46 can only be used for compatibility with old devices sold
in Japan. Modern products, such as AR6003/AR6004 don't support these channels.
Keeping them in the upstream is error prone and requires full network stack
support. A custom patch should be used in case such compatibility is required.

Without this one, a user is able to start an AP using wpa_supplicant,
for example, on one of these channels (34/38/42/46), without getting
any warning/error from the cfg80211 or ath6kl - which is correct
(since these channels match regdom rules). However, the AR6003 and its
firmware (we're using v3.4.0.225) will fail and return
"WMI_CMDERROR_EVENTID" with "INVALID_PARAM" error code.

Signed-off-by: Rostyslav Khudolii <rkhudolii@airtame.com>
Cc: Attila Sukosd <attila@airtame.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>