Get rid of now obsolte LD_PRELOAD hack

Dependencies

• [2] ZQLF4QLV Replace TestHTTPMockServer with python script
• [3] RWNXH3H2 lastModified -> lastModifiedDate
• [4] J52POHVC Update to NixOS 20.09

Change contents

• edit in flake.nix at line 348
  [3.537]→[2.29:175](∅→∅)
  −

  − export NIX_REDIRECTS=/etc/protocols=${iana-etc}/etc/protocols

  − export LD_PRELOAD="${pkgs.libredirect}/lib/libredirect.so"