Problem
Drupal 7 had two translation systems, node copy based content translation with a core UI and field based translation with a core API and a contrib UI. Drupal 8 attempts to standardise on field translation (which applies to entities of all kinds not just nodes). However, Drupal 8 still has both modules in the codebase. The legacy module is hidden from sight for new sites, but old sites will have it enabled on upgrade if it was before. While we expect contrib will stop supporting this way of translation, and it might "organically die off", if/once #1952044: Upgrade path for legacy content translation module data is resolved, we should be able to remove the module, since we keep the data related in new systems.
Proposal
Once #1952044: Upgrade path for legacy content translation module data is done, just remove the module from the codebase.
Dependencies
#1952044: Upgrade path for legacy content translation module data