fix (tests): Suppress console output in tests

[mjc1283]

Summary

Inspired by #147, this updates tests to prevent real console output that makes results hard to read.

• In general, we can create loggers with logToConsole: false to disable real output. For tests that don’t assert log calls, I used this.
• If a test was previously stubbing only to prevent real output, I removed the stub and used logToConsole: false instead.
• Some tests were stubbing both to assert log calls and to prevent real output. I mostly left these alone.
• As pointed out in fix(test): Suppress logs when NODE_ENV=test #147, real output was sometimes still happening because log was called before sinon.stub. For these, I added logToConsole: false.
• The top-level entry points (index.node.js and index.browser.js) construct loggers internally. To prevent real output in these cases, I stubbed createLogger.

Test plan

Run tests and verify that there is no unwanted real log output

[coveralls]

Coverage decreased (-0.2%) to 97.258% when pulling 1d9673d on mcarroll/clean-test-log into 4d3d40c on master.

[coveralls]

Coverage decreased (-0.2%) to 97.258% when pulling 1ddd9e0 on mcarroll/clean-test-log into 4d3d40c on master.

[mikeproeng37]

lgtm