Remove newly introduced NamespacesFromNone

[howardjohn]

#3588 added this to Gateway. I don't think it makes sense to say allowedRoutes=None -- why bother with the listener if you don't allow any routes?

This seems to have ~accidentally been added to support using it in AllowedListeners, but we added it to allowedRoutes too.

I am also not convinced its needed for AllowedListeners. The rationale seems to be to make it so the default can be 'none', but we can expressed that by AllowedListeners: nil anyways.

[darshansreenivas]

Hi @robscott, please assign me :)

[robscott]

Thanks @darshansreenivas! The actual assignment may not work here, but just as a heads up, we likely need this to be ready by Monday to allow us to keep on moving with our release process.

/assign @darshansreenivas