build: drop redundant flake smoke check (task 0003)

The checks.smoke derivation only ran 'kitchen --help', which the e2e
tier now covers (end_to_end_test.ts, '--help lists the view command').
checks.tests is the remaining flake check.

flake.nix

@@ -93,11 +93,6 @@
               doCheck = true;
               installPhase = "touch $out";
             };
-
-            smoke = pkgs.runCommand "kitchen-smoke" { } ''
-              ${kitchen}/bin/kitchen --help
-              touch $out
-            '';
           };
         };
     };