Erased methods dup and ndup from UTF8Str
Erased methods dup and ndup from UTF8Str

These were created for an earlier attempt at obtaining
error message strings from Error, and are otherwise
unused. The bindings should only wrap strings allocated by
GLib and never attempt to allocate C strings on their own.
Where an owned copy is required, it'd rather be a String.
The client code should not be encouraged to unsafely produce
UTF8Str either.

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