python3.pkgs.pip: 20.1.1 -> 20.2.4

Reproducible builds of pyproject projects using pip is resolved.

Fixes https://github.com/pypa/pip/issues/7808
Fixes https://github.com/NixOS/nixpkgs/issues/81441

The more recent c409f69480 caused trouble
with pyproject troubles and had to be reverted anyway.
https://github.com/NixOS/nixpkgs/pull/102222#issuecomment-722380794

Revert "pythonPackages.pip: make reproducible (#102222)"

This reverts commit c409f69480.

Revert "python3Packages.pip: allow setting reproducible temporary directory via NIX_PIP_INSTALL_TMPDIR"

This reverts commit aedbade43e.

pkgs/development/python-modules/bootstrapped-pip/default.nix

@@ -23,11 +23,6 @@ stdenv.mkDerivation rec {
   ];
 
   postPatch = ''
-    # Apply the pip reproducible patch
-    pushd "${pip.src.name}"
-      patch -p1 < ${../pip/reproducible.patch}
-    popd
-
     mkdir -p $out/bin
   '';