treewide: remove redundant SETUPTOOLS_SCM_PRETEND_VERSION usage

The setuptools-scm packages gained a setup hook, that sets it to the
derivation version automatically, so setting it to that manually has
become redundant.

This also affects downstream consumers of setuptools-scm, like hatch-vcs
or flit-scm.

pkgs/development/python-modules/atom/default.nix

@@ -22,8 +22,6 @@ buildPythonPackage rec {
     hash = "sha256-NXjvRVYcWU9p7b8y2ICOzYe6TeMh1S70Edy/JvTG7a4=";
   };
 
-  SETUPTOOLS_SCM_PRETEND_VERSION = version;
-
   nativeBuildInputs = [
     setuptools-scm
   ];