tty: serial_cs: remove unused struct serial_cfg_mem

tty: serial_cs: remove unused struct serial_cfg_mem

clang-struct [1] found struct serial_cfg_mem's members unused.

In fact, the whole structure is unused since commit 6ae3b84d9793
("serial_cs: use pcmcia_loop_config() and pre-determined values"). Drop
it completely.

[1] https://github.com/jirislaby/clang-struct

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20231121103626.17772-7-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>