x86/ioapic: Remove unused "IOAPIC_AUTO" define

Last use was removed more than 5 years ago, in:

   5ad274d4: ("x86/irq: Remove unused old IOAPIC irqdomain interfaces")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200724114418.629021-2-mingo@kernel.org

arch/x86/include/asm/io_apic.h

@@ -99,7 +99,6 @@ struct IR_IO_APIC_route_entry {
 struct irq_alloc_info;
 struct ioapic_domain_cfg;
 
-#define IOAPIC_AUTO			-1
 #define IOAPIC_EDGE			0
 #define IOAPIC_LEVEL			1