BaseTools: Remove './SecMain' from 'run' target

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>