Consider using Context as the unique way to specify parenthood

[carlosalberto]

At this moment, CorrelationContext and Span instances being created can explicitly specify their parent:

spanBuilder.setParent(anotherSpan);
spanBuilder.setParent(someSpanContext);

As part of OTEP 66, we could remove these and have a single one specifying Context:

// Decide the parent of whatever it is in the specified context.
spanBuilder.setParent(context);

[bogdandrutu]

For the same reasons we have a Span object (mostly for manual propagation - users that don't want to use Context we need to support the version that receives as parent a Span as well).

[jmacd]

I support this motion.

[Oberon00]

I think we should at least remove the SpanContext option, mainly because of the issues outlined in open-telemetry/oteps#58.

If we want to go further, after that, we can actually remove SpanContext completely from any public facing API (methods to get span+trace ID move to Span, sampled flag and tracestate is better hidden away in the context anyway). And then it's a small step to remove Span and replace it with tracer operations that take a context argument (see open-telemetry/oteps#73, open-telemetry/oteps#68).