serial: 8250_pci: remove rts_n override from Baytrail quirk

It should not be used together with Auto Flow Control, and
Auto Flow Control is always enabled on Baytrail.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>