python3Packages.theano-pymc: mark as broken

theano-pymc is old enough and will no longer be updated

pkgs/development/python-modules/theano-pymc/default.nix

···
     homepage = "https://github.com/majidaldo/Theano-PyMC";
     license = lib.licenses.asl20;
     maintainers = with lib.maintainers; [ nidabdella ];
+    broken = true;
   };
 }