Clean up incomplete migration guides tracking issue

At a glance, the following migration guides need work:

- [ ] [18319](https://github.com/bevyengine/bevy/pull/18319) - needs consolidation and more detail.
- [x] [17687](https://github.com/bevyengine/bevy/pull/17687) - blank
- [x] [17645](https://github.com/bevyengine/bevy/pull/17645) - remove template
- [x] [17581](https://github.com/bevyengine/bevy/pull/17581) - potentially remove
- [ ] [17567](https://github.com/bevyengine/bevy/pull/17567) - suspected incomplete
- [ ] [17215](https://github.com/bevyengine/bevy/pull/17215) - blank
- [ ] [16942](https://github.com/bevyengine/bevy/pull/16942) - blank
- [x] [16911](https://github.com/bevyengine/bevy/pull/16911) - needs detail
- [x] [16401](https://github.com/bevyengine/bevy/pull/16401) - blank
- [ ] [16279](https://github.com/bevyengine/bevy/pull/16279) - blank
- [x] [16088](https://github.com/bevyengine/bevy/pull/16088) - blank
- [x] [16082](https://github.com/bevyengine/bevy/pull/16082) - needs cleanup
- [x] [16069](https://github.com/bevyengine/bevy/pull/16069) - blank
- [x] [16050](https://github.com/bevyengine/bevy/pull/16050) - blank
- [x] [15844](https://github.com/bevyengine/bevy/pull/15844) - blank
- [x] [15482](https://github.com/bevyengine/bevy/pull/15482) - potentially redundant

I'll start working on these, but I wanted to make a record of it. Other migration guides look ok at a glance, but some may need to be revisited or consolidated. Feel free to add to the list as you find ones that need work.

Review the migration guides and linked pull requests listed in the issue, starting with PR 18319 and the entries marked blank, incomplete, or needing cleanup. Confirm which guides should be consolidated, expanded, templated, or removed, then update the tracking list so every item reflects its current state.

Written by the indexing model from the issue text.