platform/x86: fujitsu-laptop: Do not include linux/slab.h

Do not include linux/slab.h as all module code now uses managed memory
allocations and thus neither k*alloc() nor kfree() is used.

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Reviewed-by: Jonathan Woithe <jwoithe@just42.net>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>