Draft: Delete deployments_raise_updated_at_inefficient_error Feature Flag

What does this MR do and why?

!116656 (merged) introduces a breaking change in the Deployments API behind a Feature Flag (deployments_raise_updated_at_inefficient_error).

This MR deletes that Feature Flag, making the change effective for all instances of GitLab.

With the deployments_raise_updated_at_inefficient_error FF removed, queries to the Deployments API (GraphQL or REST) will result in an InefficientQueryError if an updated_at filter is not paired with order_by=updated_at.

Issue: #328500 (closed)

FF Rollout Issue: #409584 (closed)

Screenshots or screen recordings

A call to the GET /projects/:id/deployments endpoint results in a (404) Bad request if an updated_at filter is used without sorting by updated_at:

How to set up and validate locally

1. Pick any project that has a Deployment, or create a new test project and run a deploy pipeline (guide: https://docs.gitlab.com/ee/ci/environments/#environments-and-deployments)

2. Create an access token to use for API requests (guide: https://docs.gitlab.com/ee/user/profile/personal_access_tokens.html#personal-access-tokens)

3. Run the following request from the terminal:

   curl -ki -X GET \
   --header "Authorization: Bearer $ACCESS_TOKEN" \
   "https://gdk.test:3443/api/v4/projects/21/deployments?updated_after=2019-03-15T08:00:00Z"

   This should result in the following error message:

   {"message":"400 Bad request - `updated_at` filter requires `updated_at` sort"}%

4. (Optional) For comparison, run the following request for a successful API call

   curl -ki -X GET \
   --header "Authorization: Bearer $ACCESS_TOKEN" \
   "https://gdk.test:3443/api/v4/projects/21/deployments?order_by=updated_at&updated_after=2019-03-15T08:00:00Z"

MR acceptance checklist

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