ARM: GIC: ITS: remove no longer needed VCPU ID in host LPI entry

ARM: GIC: ITS: remove no longer needed VCPU ID in host LPI entry

To get easy access to the VCPU a forwarded LPI interrupt should be
injected to, so far we stored the VCPU ID in the host LPI entry.
However this creates a redundancy, since we keep the target VCPU in
the struct pending_irq already, which we can easily look up given the
domain and the virtual LPI number.
Apart from removing the redundancy this avoids having to update this
information later and keeping it in sync in a race-free fashion.
Since this information has not been used that, this patch actually does
not change anything, it just removes the declaration and initialization.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>