genirq/msi: Remove unused domain callbacks

No users and there is no need to grow them.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20211126223824.322987915@linutronix.de
Link: https://lore.kernel.org/r/20211206210224.041777889@linutronix.de