Clean up pausing logic

[bliptec]

While working on #382 I noticed there are a number of different places that telemetry is paused when trying to shut down. It'd be nice to consolidate towards only pausing once, or at least less, but this may involve refactoring or careful testing. A single flush and teardown seems to try to pause telemetry a handful of times, which makes it more difficult to reason about the SDK's behavior.

[maxgolov]

This may be related to a few topics we discussed today, e.g. #753