pythonPackages.requests: disable multiple outputs

The `dev` output is empty anyway.

The problem is that it interacts badly with other parts of python and
stdenv infrastructure. In particular, before this patch it installs
code into `out` output (with only generated `nix-support` in `dev`),
but `makePythonPath` then uses `propagatedBuildInputs` to generate
`PYTHONPATH` while stdenv selects `dev` outputs for
`propagatedBuiltInputs`. This results in `makePythonPath` linking to
the empty `dev` output in `PYTHONPATH`.

This reverts a piece of commit 28299f669a.

pkgs/development/tools/glslviewer/default.nix

@@ -22,7 +22,7 @@ stdenv.mkDerivation rec {
     libXi libX11
   ] ++ (with python2Packages; [ python setuptools wrapPython ])
     ++ stdenv.lib.optional stdenv.isDarwin Cocoa;
-  pythonPath = with python2Packages; [ requests.dev ];
+  pythonPath = with python2Packages; [ requests ];
 
   # Makefile has /usr/local/bin hard-coded for 'make install'
   preConfigure = ''