Bring the generated enum to crate's top-level namespace
Bring the generated enum to crate's top-level namespace

As the enum values are now namespaced with the enum type, there is no
need for additional module namespacing for those.

gi-rust/grust,gi-rust/gobject-sys,gi-rust/grust-proof,gi-rust/glib-sys,gi-rust/gio-sys