flake: static build in CI

That way we can automatically push the static build (compressed as
tarball) into the AFNix S3 bucket and have it updated on each update to
main.

Change-Id: I1002727ab12c0ab6b95c8d37ae4620996607d7b7

flake.nix

@@ -336,21 +336,7 @@
           }
         );
 
-        # Building Lix twice in CI is expensive, but we can catch a lot of static
-        # build regressions by at least making sure it evals and configures.
-        configure-static = lib.genAttrs linux64BitSystems (
-          system:
-          self.packages.${system}.nix-static.overrideAttrs {
-            dontBuild = true;
-            installPhase = ''
-              runHook preInstall
-
-              echo "configure-static complete. exiting with success"
-              mkdir -p "$out"
-              exit 0
-            '';
-          }
-        );
+        buildStatic = lib.genAttrs linux64BitSystems (system: self.packages.${system}.nix-static);
 
         devShell = forAllSystems (system: {
           default = self.devShells.${system}.default;