x86/acpi: remove acpi_pic_sci_set_trigger()

Remove apci_pic_set_trigger() declaration: there is no definition and there are
no calls to such function in the XEN project.

Signed-off-by: Federico Serafini <federico.serafini@bugseng.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/include/asm/acpi.h

@@ -81,7 +81,6 @@ extern bool acpi_lapic, acpi_ioapic, acpi_noirq;
 extern bool acpi_force, acpi_ht, acpi_disabled;
 extern u32 acpi_smi_cmd;
 extern u8 acpi_enable_value, acpi_disable_value;
-void acpi_pic_sci_set_trigger(unsigned int, u16);
 
 static inline void disable_acpi(void)
 {