Do not use HintPath for added metadata references

Instead of
```

..\..\Lib.dll

```

generate

```

```

@jasonmalinowski:
> I (at least, probably @jaredpar too) consider the IDE's form there to be a bug. Because in the simple case, HintPath is looked at fairly late; if the Reference Include simple name can be resolved, the HintPath often gets ignored. We've had plenty of "surprises" over the years, and honestly I wished the second was what we generated. For Roslyn, we just said the second is the only form because the first is a regret.

See full discussion on https://github.com/dotnet/arcade/pull/428#discussion_r208032449.