Remove health_status on project index

The index index_issues_on_project_health_status_asc_work_item_type has a very low usage: https://dashboards.gitlab.net/goto/DfAwhCwHR?orgId=1https://dashboards.gitlab.net/goto/DfAwhCwHR?orgId=1

It got introduced with !104094 (merged) but nowadays is barely used. Even the queries from the original MR no longer use the index.

The issues table already has lots of indexes, and as part of our guidelines we should reduce indexes as we can't support all permutations of filters and sorting options.

This is only justified for common use cases and should not be considered as a way to make all permutations of filter and sort performant. What this means practically is that there will likely be filtered views and API requests that timeout when certain sorting or filtering options are applied.