KVM: x86: Drop unused check_apicv_inhibit_reasons() callback definition

KVM: x86: Drop unused check_apicv_inhibit_reasons() callback definition

The check_apicv_inhibit_reasons() callback implementation was dropped in
the commit b3f257a84696 ("KVM: x86: Track required APICv inhibits with
variable, not callback"), but the definition removal was missed in the
final version patch (it was removed in the v4). Therefore, it should be
dropped, and the vmx_check_apicv_inhibit_reasons() function declaration
should also be removed.

Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Reviewed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Link: https://lore.kernel.org/r/54abd1d0ccaba4d532f81df61259b9c0e021fbde.1714977229.git.houwenlong.hwl@antgroup.com
Signed-off-by: Sean Christopherson <seanjc@google.com>