tty: simserial: drop unused alt_speed handling

This driver was setting the deprecated and broken alt_speed based on port
flags, but never provided a means to change the flags or to actually
change the speed.

Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>