SecurityPkg/AuthSeriableLib: Always delete variable in certdb

SecurityPkg/AuthSeriableLib: Always delete variable in certdb

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1783

While cleaning the certdb, always delete the variable data in
the certdb regardless of its attribute.

Cc: Chao Zhang <chao.b.zhang@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian Wang <jian.j.wang@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Reviewed-by: Chao Zhang <chao.b.zhang@intel.com>