Make Capture.AT-KEY 2% faster
Make Capture.AT-KEY 2% faster

This method was performing a redundant concreteness check that none of
the other methods were doing, all of which seem to work OK.

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