x86/apic: Remove X86_IRQ_ALLOC_CONTIGUOUS_VECTORS

Now that the PCI/MSI core code does early checking for multi-MSI support
X86_IRQ_ALLOC_CONTIGUOUS_VECTORS is not required anymore.

Remove the flag and rely on MSI_FLAG_MULTI_PCI_MSI.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20221111122015.865042356@linutronix.de