Fixup du tests

Disable the top-level test as it's not working well. Not clear we want
this tbh

Author: jeromekelleher

tests/test_core.py

@@ -237,7 +237,9 @@ def test_examples(self, chunk_size, size, start, stop):
         # It works in CI on Linux, but it'll probably break at some point.
         # It's also necessary to update these numbers each time a new data
         # file gets added
-        ("tests/data", 5045032),
+        # NOTE: removed this after additional plink files broke it in #390.
+        # It's not worth the trouble - see #330
+        # ("tests/data", 5053610),
         ("tests/data/vcf", 5018640),
         ("tests/data/vcf/sample.vcf.gz", 1089),
     ],