HealthCheckInterface connectionUri doesn't need to exist

[whitfin]

Currently the interfaces require connectionUri, but this only makes sense in a few cases and so I think this shouldn't be something that's in the interface itself (just the implementation of a check). I'm also not entirely sure why there needs to be two interfaces?

[whitfin]

FWIW I am more than happy to strip this out, I'm just weary of downstream modules which might depend on this and need further changes (and I'm not really using those modules).