s390/nospec: remove unneeded header includes

Commit 4efd417f298b ("s390: raise minimum supported machine generation
to z10") removed the usage of alternatives and lowcore in expolines
macros. Remove unneeded header includes as well.

With that, expoline.S doesn't require asm-offsets.h and
expoline_prepare target dependency could be removed.

Tested-by: Joe Lawrence <[e-mail]>
Link: https://lore.kernel.org/r/patch-2.threa[e-mail]
Signed-off-by: Vasily Gorbik <[e-mail]>
Signed-off-by: Alexander Gordeev <[e-mail]>

arch/s390/Makefile

···
 
 ifdef CONFIG_EXPOLINE_EXTERN
 modules_prepare: expoline_prepare
-expoline_prepare: prepare0
+expoline_prepare:
 	$(Q)$(MAKE) $(build)=arch/s390/lib/expoline arch/s390/lib/expoline/expoline.o
 endif
 endif

arch/s390/include/asm/nospec-insn.h

···
 #ifndef _ASM_S390_NOSPEC_ASM_H
 #define _ASM_S390_NOSPEC_ASM_H
 
-#include <asm/alternative-asm.h>
-#include <asm/asm-offsets.h>
 #include <asm/dwarf.h>
 
 #ifdef __ASSEMBLY__