Depend on python3-distutils when we have setuptools < 60, which doesn't use its internal distutils copy, yet.

Also Recommend build-essential, ca-certificates, and python3-dev, previously transitively depended & recommended through python3-pip.

* Drop explicit Depends on python3-pip, it's not needed. (Closes: #1019849)
* Depend on python3-distutils, instead. It was previously a transitive
  dependency through python3-pip.

Changes-By: lintian-brush
Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html

Update to upstream version '20.16.3+ds'
with Debian dir 85525cae602975edc2481bb8a98503cebe8156a8

Update to upstream version '20.15.0+ds'
with Debian dir 656b2a4c5d9d73521073e1786df0467c42942738

Update to upstream version '20.14.0+ds'
with Debian dir 3f25c4ac3ed41db5ca1455eab04b5da38ee49d9a

Update to upstream version '20.13.0+ds'
with Debian dir 63a9e3f42f3e47a4fc041d0cbac33696488b5e6d

Mark pypy and python2.7 autopkgtests as skip-not-installable for now, as the binary packages are in NEW. (Closes: #1003687)

Reorganise wheel packages, building individual wheels from their source packages (Closes: #1003573):

* Reorganise wheel packages, building individual wheels from their source
  packages (Closes: #1003573):
  - Depend on individual wheel packages.