KVM: x86: SVM: remove avic's broken code that updated APIC ID

AVIC is now inhibited if the guest changes the apic id,
and therefore this code is no longer needed.

There are several ways this code was broken, including:

1. a vCPU was only allowed to change its apic id to an apic id
of an existing vCPU.

2. After such change, the vCPU whose apic id entry was overwritten,
could not correctly change its own apic id, because its own
entry is already overwritten.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220606180829.102503-4-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>