kubernetes / kubectl: move env variable(s) into env for structuredAttrs

Need to do this together to avoid eval complaints:
"error: The `env` attribute set cannot contain any attributes passed to derivation."

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

@@ -9,7 +9,7 @@ kubernetes.overrideAttrs (_: {
     "convert"
   ];
 
-  WHAT = lib.concatStringsSep " " [
+  env.WHAT = toString [
     "cmd/kubectl"
     "cmd/kubectl-convert"
   ];

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

@@ -51,7 +51,7 @@ buildGoModule (finalAttrs: {
 
   patches = [ ./fixup-addonmanager-lib-path.patch ];
 
-  WHAT = lib.concatStringsSep " " components;
+  env.WHAT = toString components;
 
   buildPhase = ''
     runHook preBuild