irqdomain: Kill irq_domain_add_legacy_isa

This helper doesn't have a user anymore, let's remove it.
Signed-off-by: Marc Zyngier <maz@kernel.org>

Documentation/core-api/irq/irq-domain.rst

@@ -146,7 +146,6 @@ Legacy
 
 	irq_domain_add_simple()
 	irq_domain_add_legacy()
-	irq_domain_add_legacy_isa()
 	irq_domain_create_simple()
 	irq_domain_create_legacy()
 

include/linux/irqdomain.h

@@ -45,9 +45,6 @@ struct cpumask;
 struct seq_file;
 struct irq_affinity_desc;
 
-/* Number of irqs reserved for a legacy isa controller */
-#define NUM_ISA_INTERRUPTS	16
-
 #define IRQ_DOMAIN_IRQ_SPEC_PARAMS 16
 
 /**
@@ -355,14 +352,6 @@ static inline struct irq_domain *irq_domain_add_nomap(struct device_node *of_nod
 {
 	return __irq_domain_add(of_node_to_fwnode(of_node), 0, max_irq, max_irq, ops, host_data);
 }
-static inline struct irq_domain *irq_domain_add_legacy_isa(
-				struct device_node *of_node,
-				const struct irq_domain_ops *ops,
-				void *host_data)
-{
-	return irq_domain_add_legacy(of_node, NUM_ISA_INTERRUPTS, 0, 0, ops,
-				     host_data);
-}
 static inline struct irq_domain *irq_domain_add_tree(struct device_node *of_node,
 					 const struct irq_domain_ops *ops,
 					 void *host_data)