Delete obsolete project_selector store module

The project_selector store module seems to be obsolete and we might be able to remove it altogether. Let's make sure it's not used anywhere anymore, and delete the related code if it isn't.

How to verify

1. Go to your instance's security dashboard -/security/dashboard and check point 3 below
2. Go to a group's security dashboard (Group -> "Security & Compliance" -> "Security Dashboard") and check point 3 below
3. Make sure the "Project security status" widget renders as expected (showing data, can be interacted with, no console errors)