Resolve Delayed Job testing TODO

[kaylareopelle]

The Delayed Job tests have the following TODO:

newrelic-ruby-agent/test/multiverse/suites/delayed_job/before_suite.rb

Lines 23 to 25 in c91b9ce

	# TODO: Core Technology - guess_backend is deprecated on some versions,
	# required on others.
	Delayed::Worker.guess_backend

we should research the introduction of that TODO to see if it is still applicable and if any work needs to be done. Do work if needed. Remove the TODO in any case.

[workato-integration]

https://issues.newrelic.com/browse/NEWRELIC-3637