Features defined in versioned CPU model are recorded in env->user_features
since they are updated as property. It's unwated because they are not
user specified.

Simply clear env->user_features as a fix. It won't clear user specified
features because user specified features are filled to
env->user_features later in x86_cpu_expand_features().

Cc: Chenyi Qiang <chenyi.qiang@intel.com>
Suggested-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NXiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20200713174436.41070-2-xiaoyao.li@intel.com>
[ehabkost: fix coding style]
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>