gpio: remove broken irq_to_gpio() interface

gpiolib has removed the irq_to_gpio() API several years ago,
but the global header still provided a non-working stub.

To prevent new users of this broken function from showing
up, let's remove the stubs as well.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio.h

@@ -70,11 +70,6 @@ static inline int gpio_to_irq(unsigned int gpio)
 	return __gpio_to_irq(gpio);
 }
 
-static inline int irq_to_gpio(unsigned int irq)
-{
-	return -EINVAL;
-}
-
 #endif /* ! CONFIG_ARCH_HAVE_CUSTOM_GPIO_H */
 
 /* CONFIG_GPIOLIB: bindings for managed devices that want to request gpios */
@@ -222,13 +217,6 @@ static inline void gpiochip_unlock_as_irq(struct gpio_chip *chip,
 	WARN_ON(1);
 }
 
-static inline int irq_to_gpio(unsigned irq)
-{
-	/* irq can never have been returned from gpio_to_irq() */
-	WARN_ON(1);
-	return -EINVAL;
-}
-
 static inline int
 gpiochip_add_pin_range(struct gpio_chip *chip, const char *pinctl_name,
 		       unsigned int gpio_offset, unsigned int pin_offset,