target/i386: Remove split lock detect in Snowridge CPU model

At present, there's no mechanism intelligent enough to virtualize split
lock detection correctly. Remove it in Snowridge CPU model to avoid the
feature exposure.

Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
Message-Id: <20210630012053.10098-1-chenyi.qiang@intel.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>