Drop VMX's global list of user return MSRs now that VMX doesn't resort said
list to isolate "active" MSRs, i.e. now that VMX's list and x86's list have
the same MSRs in the same order.

In addition to eliminating the redundant list, this will also allow moving
more of the list management into common x86.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-11-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>