Delete the work_items_view_preference feature flag

This feature flag was introduced in 16.4, which is more than 4 milestones ago.

As part of our process we want to ensure feature flags don't stay too long in the codebase.

Rollout issue: #482931 (closed)

Remaining mentions of the feature flag (click to expand)

doc/user/project/issues/issue_work_items.md
18:- [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/9584) in GitLab 17.5 [with a flag](../../../administration/feature_flags.md) named `work_items_view_preference`. Disabled by default. This feature is in [beta](../../../policy/development_stages_support.md#beta).

doc-locale/ja-jp/user/project/issues/managing_issues.md
490:- [Generally available](https://gitlab.com/gitlab-org/gitlab/-/issues/482931) in GitLab 18.2. Feature flag `work_items_view_preference` removed.

doc/user/project/issues/issue_work_items.md
18:- [Introduced](https://gitlab.com/groups/gitlab-org/-/epics/9584) in GitLab 17.5 [with a flag](../../../administration/feature_flags.md) named `work_items_view_preference`. Disabled by default. This feature is in [beta](../../../policy/development_stages_support.md#beta).
19:- Feature flag named `work_items_view_preference` enabled on GitLab.com in GitLab 17.9 for a subset of users.
20:- Feature flag named `work_items_view_preference` [enabled](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/184496) on GitLab.com, GitLab Self-Managed, and GitLab Dedicated in 17.10.
22:- [Generally available](https://gitlab.com/gitlab-org/gitlab/-/issues/482931) in GitLab 18.2. Feature flag `work_items_view_preference` removed.

Currently the feature flag is enabled on production

It is possible that this MR will still need some changes to remove references to the feature flag in the code. At the moment the gitlab-housekeeper is not always capable of removing all references so you must check the diff and pipeline failures to confirm if there are any issues. It is the responsibility of groupproject management to push those changes to this branch. If they are already removing this feature flag in another merge request then they can just close this merge request and add intended_to_rollout_by date in the yml file.

TODO for the reviewers before merging this MR

• See the status of the rollout by checking #482931 (closed), https://gitlab.com/gitlab-com/gl-infra/feature-flag-log/-/issues/?search=work_items_view_preference&sort=created_date&state=all&label_name%5B%5D=host%3A%3Agitlab.com
• Verify the feature flag status via chatops by running /chatops run feature get work_items_view_preference.
• Search for references to WorkItemsViewPreference in frontend part of code
• Search for references to work_items_view_preference in code
• Check if we need to remove any Gem or other related code by looking at the changes in !165085 (merged)

This change was generated by gitlab-housekeeper using the Keeps::DeleteOldFeatureFlags keep.

To provide feedback on your experience with gitlab-housekeeper please create an issue with the label GitLab Housekeeper and consider pinging the author of this keep.