driver core: remove drivers/base/sys.c and include/linux/sysdev.h

Now that all users of 'struct sysdev' are removed from the kernel, we
can safely remove the .h and .c files for this code, to ensure that no
one accidentally starts to use it again.

Many thanks for Kay who did all the hard work here on making this
happen.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>