KVM: x86: Remove some unused declarations

Commit 238adc77 ("KVM: Cleanup LAPIC interface") removed
kvm_lapic_get_base() but leave declaration.

And other two declarations were never implenmented since introduction.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20240830022537.2403873-1-yuehaibing@huawei.com


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