Deprioritize Issue checklist item counts

Summary

The current "checklist items" counts are given significant priority, appearing in the list and in the issue header. With the addition of Tasks objects these counts now compete conceptually, further highlighting that checklist items are overprioritized in the UI. Merge Requests contain the same functionality but display the count only in the list.

Add a count of child items including completion... (#369905) should be prioritized in list views over this information.

Potential Direction

Shift to Description metadata

Checklist items exist within the description, and if this detail continues to provide value it could be placed alongside "Edited" as part of the description metadata. The count would be removed from issue lists.

Checklist and edited	Checklist	Edited	Checklist complete (optional)

Availability and Testing

Job e2e:package-and-test will need to be run in the MR(s) that introduce(s) the change.

Ensure test coverage in unit/integration tests.