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>