quack_init() using deprecated API

[djziegler]

quack_init is calling DuckDB.LoadExtension(), which is documented suchly:

// DEPRECATED function that some extensions may still use to call their own Load method from the
// _init function of their loadable extension. Don't use this. Instead opt for a static LoadInternal function called
// from both the _init function and the Extension::Load. (see autocomplete extension)
// TODO: when to remove this function?

So the body of quack_init should just be a call to the LoadInternal function already implemented in the same file.