Do note that a warning symbol on top of a reference doesn't mean that it's unresolvable. Instead it means that there was some error, possibly inability to resolve, for that reference. For instance if you add a Condition
property to the reference VS will show it with the warning symbol but the assembly is still resolvable.
The only way to know if the reference can be removed is to
- Remove it
- Rebuild
- Run all tests
If they all pass then you can say with a high degree of confidence that it is no longer needed