* feat: [AA-922] remove deprecated Goals backend
While the new Weekly Learning Goals were being rolled out, the previous goal setting feature still existed behind a waffle flag.
The Weekly Learning Goals now become the one and only learning goal feature.
This change does not remove the old goals feature from the legacy backend, and therefore it does not remove any of the data that was used by the old goals feature.
The goals are now driven by the single pre-existing Waffle flag ENABLE_COURSE_GOALS
- Removed COURSE_GOALS_NUMBER_OF_DAYS_GOALS waffle flag, replacing it where needed with the existing ENABLE_COURSE_GOALS
- modified the API to remove the old goal_options, keeping the redundant weekly_learning_goal_enabled flag
- updated tests
- refactor tests to fit 50 line limit in lint
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