x86: Remove more unmodified io_apic_ops

io_apic_ops.init() is either NULL, if IO-APIC support is disabled at
compile time or native_io_apic_init_mappings(). No point to have that
as we can achieve the same thing with an empty inline.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/include/asm/x86_init.h

@@ -180,7 +180,6 @@ struct x86_msi_ops {
 };
 
 struct x86_io_apic_ops {
-	void		(*init)   (void);
 	unsigned int	(*read)   (unsigned int apic, unsigned int reg);
 	void		(*disable)(void);
 };