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 6ae3b84d
("serial_cs: use pcmcia_loop_config() and pre-determined values"). Drop
it completely.

[1] https://github.com/jirislaby/clang-structSigned-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.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/serial_cs.c

@@ -90,12 +90,6 @@ struct serial_info {
 	const struct serial_quirk *quirk;
 };
 
-struct serial_cfg_mem {
-	tuple_t tuple;
-	cisparse_t parse;
-	u_char buf[256];
-};
-
 /*
  * vers_1 5.0, "Brain Boxes", "2-Port RS232 card", "r6"
  * manfid 0x0160, 0x0104