KVM: x86/mmu: Delete the "dbg" module param

Delete KVM's "dbg" module param now that its usage in KVM is gone (it
used to guard pgprintk() and rmap_printk()).

Link: https://lore.kernel.org/r/20230729004722.1056172-4-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>