Remove sampling decision from runtime

[Jeymisson]

What is the purpose of this pull request?

Node runtime is overriding jaeger-agent sampling decision. It is also creating dangling RootSpans anytime a current application doesn't receive a RootSpan from the parent request, e.g: Kuberouter.

This PR removes sampler configs enabling the default behavior, which is:

Remote (sampler.type=remote, which is also the default) sampler consults jaeger-agent for the appropriate sampling strategy to use in the current service. This allows controlling the sampling strategies in the services from a central configuration in Jaeger backend (see Remote Sampling), or even dynamically (see Adaptive Sampling).

It also only creates tracing spans when a RootSpan comes from the Router.

What problem is this solving?

How should this be manually tested?

Screenshots or example usage

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Requires change to documentation, which has been updated accordingly.