Remove mi_parser unit test

This test used to compare formatted versions of ocaml values large
enough to make understanding and updating the output impossible.

The expected values can't easily be converted to non-string values
because they do not correspond to the actual type (the 'pp' function
loses information), which is too complicated and unstable to be written
manually.

I think this test is not necessary, mli support is covered by the
black-box tests.

Author: Julow

test/lib/test_mdx_lib.ml

@@ -8,5 +8,4 @@ let () =
       Test_syntax.suite;
       Test_util.suite;
       Test_part.suite;
-      Test_mli_parser.suite;
     ]