Remove functionality that should be delegated to the OpenTelemetry SDK / Exporters

[trask]

Remove functionality that should be delegated to the OpenTelemetry SDK / Exporters:

• Sampling (Remove sampling #17)
• Trace context propagation formats (Remove propagation formats #24)
• Service name split by tags (Remove service name split by tags #20)
• Service name mappings (Remove service name mappings #23)
• Trace interceptors (Remove trace interceptors #21)
• Exporter (Remove exporter #25)
• Report hostname (Remove report hostname #31)
• Globally applied tags (Remove globally applied tags #32, Remove thread name and thread id tags #42)
• Remove tag decorators (Remove service name decorators #33, Remove resource name decorators #34, Remove operation name decorators #36, Remove error flag decorator #37, Remove span type decorators #38, Remove decorators infrastructure #39)

[trask]

For the Tag decorators, it's not clear to me whether this functionality should eventually be absorbed by the individual instrumentations, or by the SDK / Exporter, or a mix.

So thinking of keeping the tag decorators mostly as is for now.

[trask]

I've looked at the decorators in more detail, and ready to go ahead and remove them, absorbing a bit of their functionality into the individual instrumentation where it seems appropriate.

[trask]

Closing, I think this issue is completed now! A few more things will fall out as part of #6 (Remove OpenTracing interoperability) and #43 (Change instrumentation to use OpenTelemetry API indirectly).