Fixes --clean-todo flag to actually do the cleaning

[scalvert]

The --clean-todo flag was missing from the todo-handler, resulting in this flag effectively being a noop. This fix ensures that both --clean-todo and --fix work for cleaning todos, though we prefer users run the narrowly scoped --clean-todo, as it changes less and results in more predictable effects.

[MelSumner]

Confirmed that this works to resolve the issue (pulled the branch down, used yarn link, and went through the workflow).