sandbox: Drop unnecessary test node

The spl-test4 node deliberately has an invalid compatible string. This
causes a warning from dtoc and the check it does is not really necessary.
Drop it, to avoid the warning and associated confusion.

Signed-off-by: Simon Glass <sjg@chromium.org>

test/py/tests/test_ofplatdata.py

@@ -17,7 +17,6 @@ def test_spl_devicetree(u_boot_console):
     assert "u-boot,dm-spl" not in output
     assert "u-boot,dm-tpl" not in output
 
-    assert "spl-test4" in output
     assert "spl-test5" not in output
     assert "spl-test6" not in output
     assert "spl-test7" in output