x86/apb_timer: Drop unused declaration and macro

Drop an extern declaration that has never been used and a no longer
needed macro.
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200513100944.9171-2-johan@kernel.org

arch/x86/include/asm/apb_timer.h

@@ -25,10 +25,7 @@
 #define APBT_MIN_FREQ          1000000
 #define APBT_MMAP_SIZE         1024
 
-#define APBT_DEV_USED  1
-
 extern void apbt_time_init(void);
-extern int arch_setup_apbt_irqs(int irq, int trigger, int mask, int cpu);
 extern void apbt_setup_secondary_clock(void);
 
 extern struct sfi_timer_table_entry *sfi_get_mtmr(int hint);