x86/spectre_v2: Remove remaining references to lfence mitigation

x86/spectre_v2: Remove remaining references to lfence mitigation

The LFENCE mitigation alone was deemed to be insufficient and the
related code was mostly removed by commit cf3b86bc07619
(Revert "x86/spec_ctrl: Add 'nolfence' knob to disable fallback for
spectre_v2 mitigation")

This patch cleans up two additional references that still exist.

Orabug: 28631590
CVE: CVE-2018-15572

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Mark Kanda <mark.kanda@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>