USB: serial: ti_usb_3410_5052: drop closing_wait module parameter

The ti_usb_3410_5052 has supported changing the closing_wait parameter
through TIOCSSERIAL (setserial) for about a decade and commit
f1175daa ("USB: ti_usb_3410_5052: kill custom closing_wait").

It's time to drop the corresponding driver-specific module parameter.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>