misc: vmw_vmci: Remove unused vmci_doorbell_notify

vmci_doorbell_notify() was added in 2013 by
commit 83e2ec76 ("VMCI: doorbell implementation.")

but has remained unused.

Remove it.

Signed-off-by: "Dr. David Alan Gilbert" <linux@treblig.org>
Link: https://lore.kernel.org/r/20250614010344.636076-3-linux@treblig.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>