Revert "FEATURE: Introduce theme/component QUnit tests (#12517)" (PR #12632)

This reverts commit FEATURE: Introduce theme/component QUnit tests (#12517) · discourse/discourse@a53d8d3 · GitHub and FIX: Prevent double slashes in Ember templates paths (#12630) · discourse/discourse@1056344 · GitHub.

Reverted because the change broke some components. Will be added back in a few days.

GitHub