tox: remove requires: pip>=20.3.1

bluetech · bluetech · commit f237b077fc83 · 2020-12-12T18:31:52.000+02:00
Causes some trouble in CI and not really needed as old pip should still
work.
diff --git a/tox.ini b/tox.ini
@@ -16,7 +16,6 @@ envlist =
     py37-freeze
     docs
     docs-checklinks
-requires = pip >= 20.3.1
 
 [testenv]
 commands =
