[Response Ops][Task Manager] Can we remove the middleware hooks

[ymao1]

Task manager provides the ability to specify middleware hooks that modify the task instance at different points in its lifecycle. Specifically beforeSave that modifies the task instance before persisting it and beforeRun that modifies the task instance loaded from disk before running it. These hooks are currently only used in the task manager functional tests (and the only thing that they're testing is whether the hooks are called as expected). Can we remove them altogether?

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)