1. Remove the check for duplicated UserExtension section.

assigned-by: Hess Chen (hesheng.chen@intel.com)
reviewed-by: Fei Chen (feix.a.chen@intel.com)

git-svn-id: https://edk2-buildtools.svn.sourceforge.net/svnroot/edk2-buildtools/trunk/BaseTools@2576 c2973edb-eda0-4c78-bc6a-9341b269661f