s390/vdso: remove orphaned declarations

Remove couple of declarations which are unused since commit 4bff8cb545
("s390: convert to GENERIC_VDSO").

Acked-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/vdso.h

@@ -35,9 +35,7 @@ struct vdso_per_cpu_data {
 };
 
 extern struct vdso_data *vdso_data;
-extern struct vdso_data boot_vdso_data;
 
-void vdso_alloc_boot_cpu(struct lowcore *lowcore);
 int vdso_alloc_per_cpu(struct lowcore *lowcore);
 void vdso_free_per_cpu(struct lowcore *lowcore);