restructuredtext-lint is not needed to run tests.

--- pytest_regressions-2.6.0/setup.py.orig
+++ pytest_regressions-2.6.0/setup.py
@@ -34,7 +34,6 @@
             "numpy",
             "pillow",
             "pyarrow",
-            "restructuredtext-lint",
             "tox",
         ],
         "num": [