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

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1561

This patch is related to commit 9ca1f1
It's to remove the second .SecMain call from 'run' target.

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>