irqdomain: Remove unused of_device_id forward declaration

There is no users of of_device_id in irqdomain.h. Drop it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20201030165919.86234-2-andriy.shevchenko@linux.intel.com