Deprecate `hints` parameter

[TheMarex]

The hints parameter is probably one of the worst concepts of our API that exposes internal data structures to the client and allows them to pass this information back to us. This breaks a few encapsulations, means we need to ship a clunky Base64 encoder and have our internal PhantomNode size impact the size of our response objects.

It is straight forward to remove this parameter from the HTTP API but the C++ API is another problem. Since we encode internal state in the Hints object that is part of a public interface, we can't just remove this class. I don't see an easy way to do this without breaking the API.

[daniel-j-h]

Related:

• generate hints api flag https://github.com/Project-OSRM/osrm-backend/pull/3456
• v6 api list https://github.com/Project-OSRM/osrm-backend/issues/3298
• osm id as hint https://github.com/Project-OSRM/osrm-backend/issues/3219