🧪 Drop the requires section from tox.ini

Tox's self-provisioning has a bug when it is invoked with
`--installpkg` [[1]] that makes Tox hang on teardown.

The proposed workaround is making all these requirements available in
the same env Tox is installed. This patch gets rid of them instead.

[1]: tox-dev/tox#3600

Author: webknjaz

tox.ini

@@ -1,10 +1,6 @@
 [tox]
 envlist = python
 minversion = 3.21.0
-requires =
-  setuptools >= 40.9.0
-  pip >= 19.0.3
-  # tox-venv >= 0.4.0
 isolated_build = true