SecurityPkg: deprecate RpmcLib and VariableKeyLib

SecurityPkg: deprecate RpmcLib and VariableKeyLib

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2594

There's no real usage of these two libraries. They're deprecated.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Nishant C Mistry <nishant.c.mistry@intel.com>
Cc: Judah Vang <judah.vang@intel.com>
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Acked-by: Michael D Kinney <michael.d.kinney@intel.com>