Revert "Enable pytest-cov[toml] akin to upstream coverage[toml]"

This reverts commit f7bdfcf.

Author: ionelmc

setup.py

@@ -142,9 +142,7 @@ def run(self):
             'six',
             'pytest-xdist',
             'virtualenv',
-        ],
-        # Enable pyproject.toml support.
-        'toml': ['coverage[toml]'],
+        ]
     },
     entry_points={
         'pytest11': [