mt76x0: use mt76u_mcu_send_msg utility routine to send fw cmds

Use mt76u_mcu_send_msg/__mt76u_mcu_send_msg utility routines to
send commands to usb mcu. Remove following unused routines:
- mt76x0_mcu_wait_resp
- __mt76x0_mcu_msg_send
- mt76x0_mcu_msg_send
- mt76x0_dma_skb_wrap_cmd
- trace_mt_mcu_msg_send_cs
- mt76x0_mcu_cmd_deinit

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>