fetchPypi: move to top level

fetchPypi doesn't use python under the hood and doesn't need to be tied
to a specific version of python. Moving it to top level makes it more
consistent with other fetchers and makes code generation easier.

pkgs/development/interpreters/python/python-packages-base.nix

@@ -41,8 +41,6 @@ let
   # See build-setupcfg/default.nix for documentation.
   buildSetupcfg = import ../../../build-support/build-setupcfg self;
 
-  fetchPypi = callPackage ./fetchpypi.nix { };
-
   # Check whether a derivation provides a Python module.
   hasPythonModule = drv: drv?pythonModule && drv.pythonModule == python;
 
@@ -89,7 +87,7 @@ in {
   inherit lib pkgs stdenv;
   inherit (python.passthru) isPy27 isPy37 isPy38 isPy39 isPy310 isPy311 isPy3k isPyPy pythonAtLeast pythonOlder;
   inherit buildPythonPackage buildPythonApplication;
-  inherit fetchPypi;
+  inherit (pkgs) fetchPypi;
   inherit hasPythonModule requiredPythonModules makePythonPath disabled disabledIf;
   inherit toPythonModule toPythonApplication;
   inherit buildSetupcfg;