Remove xfail from a weird but passing test

Author: uranusjr

tests/functional/test_install_reqs.py

@@ -213,7 +213,7 @@ def test_multiple_constraints_files(script, data):
     assert "installed Upper-1.0" in result.stdout
 
 
-@pytest.mark.xfail(reason="Unclear what this guarantee is for.")
+# FIXME: Unclear what this guarantee is for.
 def test_respect_order_in_requirements_file(script, data):
     script.scratch_path.joinpath("frameworks-req.txt").write_text(
         textwrap.dedent(