wifi: libertas: cmd: remove unused functions

lbs_get_snmp_mib(), lbs_set_power_adapt_cfg(), lbs_set_tpc_cfg()
and lbs_set_tx_power() have been unused since 2010's
commit e86dc1ca ("Libertas: cfg80211 support").

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20250121013300.433538-3-linux@treblig.org