Do not attempt CAT PTT commands on the Icom IC-706mkIIG

This rig doesn't have PTT commands and having them there causes errors
since they  are used by the  front end API even  if RTS or DTR  PTT is
selected.

icom/ic706.c

@@ -572,8 +572,6 @@ const struct rig_caps ic706mkiig_caps = {
 .set_mem =  icom_set_mem,
 .vfo_op =  icom_vfo_op,
 .scan =  icom_scan,
-.set_ptt =  icom_set_ptt,
-.get_ptt =  icom_get_ptt,
 .get_dcd =  icom_get_dcd,
 .set_ts =  icom_set_ts,
 .set_rptr_shift =  icom_set_rptr_shift,