Removed deprecated license-file from setup.cfg.

Starting with wheel 0.32.0 (2018-09-29), the "license-file" option is
deprecated. LICENSE is now included automatically.

setup.cfg

@@ -14,6 +14,3 @@ include_trailing_comma = true
 known_first_party = django
 line_length = 79
 multi_line_output = 5
-
-[metadata]
-license-file = LICENSE