BaseTools: Remove './SecMain' from 'run' target
    
    BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1561
    
    When a target of 'run' is passed into build.py,
    BaseTools unconditionally attempts to execute the
    application called './SecMain' in the build output directory.
    
    This behavior applies to the Nt32Pkg which is being
    replaced with features in the EmulatorPkg.
    
    Signed-off-by: Bob Feng <bob.c.feng@intel.com>
    Cc: Liming Gao <liming.gao@intel.com>
    Cc: Michael D Kinney <michael.d.kinney@intel.com>
    Reviewed-by: Liming Gao <liming.gao@intel.com>
    Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>