kubectl: avoid overriding env (#491694)

pkgs/by-name/ku/kubectl/package.nix

@@ -1,6 +1,13 @@
 { lib, kubernetes }:
-
-kubernetes.overrideAttrs (_: {
+let
+  kubernetes' = kubernetes.override {
+    components = [
+      "cmd/kubectl"
+      "cmd/kubectl-convert"
+    ];
+  };
+in
+kubernetes'.overrideAttrs (_: {
   pname = "kubectl";
 
   outputs = [
@@ -9,11 +16,6 @@ kubernetes.overrideAttrs (_: {
     "convert"
   ];
 
-  env.WHAT = toString [
-    "cmd/kubectl"
-    "cmd/kubectl-convert"
-  ];
-
   installPhase = ''
     runHook preInstall
     install -D _output/local/go/bin/kubectl -t $out/bin