isdn: remove spellcaster driver

The 'sc' ISDN driver relies on using readl() to access ISA I/O memory.
This has been deprecated and produced warnings since linux-2.3.23,
disabled by default since 2.4.10 and finally removed in 2.6.5.

I found this because the compiling the driver for ARM produces
a warning:

In file included from ../drivers/isdn/sc/includes.h:8:0,
                 from ../drivers/isdn/sc/init.c:13:
../arch/arm/include/asm/io.h:115:21: note: expected 'const volatile void *' but argument is of type 'long unsigned int'

It is pretty clear that this driver has not been used for a long time
and there is no point fixing it now, so let's remove it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>