Revert "Lazy load metrics listener (#320)"

[joeyzhao2018]

This reverts commit 47c5508488eb67f6a5cdf5c25a73e4971edf02f9.

What does this PR do?

Revert the commit 47c55084 as it is causing the metrics and traces not sent. The tests done for the original commit 47c55084 was not correctly setup and caused confusion.

Motivation

Testing Guidelines

Additional Notes

Types of Changes

• [x] Bug fix
• [ ] New feature
• [ ] Breaking change
• [ ] Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• [ ] This PR's description is comprehensive
• [ ] This PR contains breaking changes that are documented in the description
• [ ] This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• [ ] This PR impacts documentation, and it has been updated (or a ticket has been logged)
• [ ] This PR's changes are covered by the automated tests
• [ ] This PR collects user input/sensitive content into Datadog
• [ ] This PR passes the integration tests (ask a Datadog member to run the tests)