Remove duplicated logger silencing

[jameslamb]

Every one of our test files contains something like this:

# Configure logger (suppress all logs in testing)
# expect_silents only work with this logger turned off; only alerts with warnings
loggerOptions <- futile.logger::logger.options()
if (!identical(loggerOptions, list())){
    origLogThreshold <- loggerOptions[[1]][['threshold']]
} else {
    origLogThreshold <- futile.logger::INFO
}
futile.logger::flog.threshold(0)

See my comment on #166 ...I think it could be beneficial to add this code to setupTestEnv one time to reduce duplicated code in the project and to lower the barrier to entry for developers writing new tests on the project (one less convention to learn!).

Thoughts?