ACPI: scan: Remove unneeded header linux/nls.h

Code that use linux/nls.h was moved to device_sysfs.c by commit
c2efefb3 ("ACPI / scan: Move sysfs-related device code to a separate file")

Remove this include so that complier has easier times and it would be
easier to grep where nls code is used.

Signed-off-by: Kari Argillander <kari.argillander@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>