Revert "Work around existing bug exposed by mixin caching."
Revert "Work around existing bug exposed by mixin caching."

This reverts commit 8ec84b608d0b3c21ec465352eef617581ed5af41.

Adding some logging showed that `self.is_composed($obj)` is always true
when building Rakudo.

rakudo/rakudo,rakudo/rakudo,tbrowder/rakudo,labster/rakudo,tbrowder/rakudo,tbrowder/rakudo,softmoth/rakudo,nbrown/rakudo,MasterDuke17/rakudo,labster/rakudo,salortiz/rakudo,nbrown/rakudo,salortiz/rakudo,MasterDuke17/rakudo,nbrown/rakudo,salortiz/rakudo,tbrowder/rakudo,tony-o/rakudo,MasterDuke17/rakudo,rakudo/rakudo,tbrowder/rakudo,softmoth/rakudo,MasterDuke17/rakudo,tony-o/rakudo,salortiz/rakudo,labster/rakudo,tony-o/rakudo,MasterDuke17/rakudo,rakudo/rakudo,nbrown/rakudo,salortiz/rakudo,softmoth/rakudo,tony-o/rakudo,nbrown/rakudo,labster/rakudo,nbrown/rakudo,salortiz/rakudo,tony-o/rakudo,rakudo/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,softmoth/rakudo,tony-o/rakudo,softmoth/rakudo,labster/rakudo,rakudo/rakudo,labster/rakudo