poetry: remove "broken" mark

Apparently it was marked by mistake in 5aa4b1994629;
it seems fine both locally and on Hydra's three platforms.

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

@@ -87,6 +87,5 @@ in buildPythonPackage rec {
     description = "Python dependency management and packaging made easy";
     license = licenses.mit;
     maintainers = with maintainers; [ jakewaksbaum ];
-    broken = true;
   };
 }