Finish removing pickle parameters from existing tasks

[markstory]

Before we can move tasks from celery to taskworker they need to not rely on pickle for parameter serialization. There are still a handful of tasks that require pickle for parameters. The tasks in LEGACY_PICKLE_TASKS should be refactored so that they are JSON safe.

• Update tasks in LEGACY_PICKLE_TASKS to have JSON safe parameters. This will take two deploys for each task to preserve backwards compatibility.
• Enable CELERY_COMPLAIN_ABOUT_BAD_USE_OF_PICKLE in s4s to further validate that no celery tasks are using pickle parameters.