UnitTestFrameworkPkg: Disable EBC in DSC file

UnitTestFrameworkPkg: Disable EBC in DSC file

https://bugzilla.tianocore.org/show_bug.cgi?id=2514

Remove EBC as one of the supported architectures
in the UnitTestFrameworkPkg DSC file.  The EBC
compiler does not support vararg macros and the
UnitTestLib class uses this feature.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Bret Barkelew <Bret.Barkelew@microsoft.com>