Before this change `mkRenamedOptionModule` would override option defaults
even when the old option name is left unused. For instance
```nix
{
optios = {
services.name.new = mkOption {
default = { one = {}; };
};
};
imports = [
(mkRenamedOptionModule [ "services" "name" "old" ] [ "services" "name" "new" "two" ])
];
config = {};
}
```
would evaluate to
`{ config.services.name.new = { two = {}; }; }`
when you'd expect it to evaluate to
`{ config.services.name.new = { one = {}; }; }`.
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