Remove unused/unimplemented/unhelpful 5to6 messages
Remove unused/unimplemented/unhelpful 5to6 messages

Also tweak some messages to reflect reality.

Part of #1356.

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