Remove correct_work_item_type feature flags

What does this MR do and why?

We are removing two feature flags:

• issues_use_correct_work_item_type_id
• issues_set_correct_work_item_type_id

Removing them together as issues_set_correct_work_item_type_id depends on issues_use_correct_work_item_type_id. I didn't remove issues_use_correct_work_item_type_id first as I wanted to be able to fully go back to using the original column issues.work_item_type_id in the event something didn't work as expected. Also, these 2 removals should be released together, so it's safer to remove them in the same MR.

In some instances, workItemType.id values might change in the GraphQL API. Now all work item type values will be 1 through 9. But in .com for example, the ids were in this state

    name     |    id    | correct_id
-------------+----------+------------
 Issue       |        1 |          1
 Incident    |        2 |          2
 Test Case   |        3 |          3
 Requirement |        4 |          4
 Task        |        5 |          5
 Objective   | 46657152 |          6
 Key Result  | 46657153 |          7
 Epic        | 91413915 |          8
 Ticket      | 91413916 |          9

We have also added a fallback mechanism in the GraphQL API (the only place where we use work item type IDs as input) so that if you provide and old ID like 46657152 for the objective type, we will still find it in the database and work as expected. This fallback will be removed in a couple of releases.

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Related to #504064 (closed)