Chore: Remove old/invalid Homepage projects

[KevinMulhern]

Because:

• We previously changed the instructions to clarify the solution learners submit for the Homepage project should not be their personal portfolio. But, many of the older submission are still personal portfolios, and we think they could be causing some confusion with learners submitting new solutions.

This commit

• Adds a data migration to remove any solutions attached to the Homepage project that were submitted more than 3 months ago.

Pull Request Requirements

• [x] I have thoroughly read and understand The Odin Project Contributing Guide
• [x] The title of this PR follows the keyword: brief description of change format, using one of the following keywords:
  • Feature - adds new or amends existing user-facing behavior
  • Chore - changes that have no user-facing value, refactors, dependency bumps, etc
  • Fix - bug fixes
• [x] The Because section summarizes the reason for this PR
• [x] The This PR section has a bullet point list describing the changes in this PR
• [x] I have verified all tests and linters pass after making these changes.
• [x] If this PR addresses an open issue, it is linked in the Issue section
• [x] If applicable, this PR includes new or updated automated tests

[KevinMulhern]

This has been tested against a copy of production locally. We'll have 178 remaining submissions for the project when the task has finished running.

Task to run on Heroku: rails data_migrations:remove_old_homepage_submissions