Revert "kvm: detect assigned device via irqbypass manager"

Now that KVM explicitly tracks the number of possible bypass IRQs, and
doesn't conflate IRQ bypass with host MMIO access, stop bumping the
assigned device count when adding an IRQ bypass producer.

This reverts commit 2edd9cb7.

Link: https://lore.kernel.org/r/20250523011756.3243624-5-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>