Remove JSON .NET unification

Opening this issue to track work that needs to happen across a few different components, enabling us to remove the unification behavior that currently exists in the host for this dependency.

At a high level, the following needs to happen:
- Update HTTP (other bindings for consistency, but HTTP is required) to remove the host dependent binding on JSON.NET and use the appropriate abstractions
- Update host pinning configuration
- Add compatibility flag to support migration/ensure existing behavior is maintained

/cc @mattchenderson