Remove obsolete references_dts0 test

[Jon Loeliger]

> The only purpose of the dtc_references_dts0 testcase was to check
> handling of references in the old dts v0 syntax.  Since we no longer
> support the old syntax, and the references_dts0.dts has been converted
> to the new format, it's entirely redundant.  This patch removes it.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.