media: rc: nuvoton: remove rudimentary transmit functionality

Transmit support in this driver was never tested and based on the code
it can't work. Just one example:
The buffer provided to nvt_tx_ir holds unsigned int values in
micro seconds: First value is for a pulse, second for a pause, etc.
Bytes in this buffer are copied as-is to the chip FIFO what can't work
as the chip-internal format is totally different. See also conversion
done in nvt_process_rx_ir_data.

Even if we would try to fix this we have the issue that we can't test
it. There seems to be no device on the market using IR transmit with
one of the chips supported by this driver.

To facilitate maintenance of the driver I'd propose to remove the
rudimentary transmit support.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>