Clean up GLQL-related feature flags
## Overview
Review and clean up GLQL-related feature flags that have been enabled for some time and may be ready for removal.
## Feature Flags to Review
1. **glql_work_items** - Enabled by default for quite some time with mostly resolved performance problems, candidate for removal - DRI @kivikakk - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/225241+s
* Also in GLQL itself: https://gitlab.com/gitlab-org/glql/-/merge_requests/336+
3. **glql_es_integration** - Enabled for some time with few recent bugs, candidate for removal - DRI @vanessaotto - ~~https://gitlab.com/gitlab-org/gitlab/-/merge_requests/225304~~ - Stuff happened! see note https://gitlab.com/gitlab-org/gitlab/-/issues/591123#note_3135366721
4. **glql_load_on_click** - Introduced as a safety measure during production readiness review, may need negotiation but candidate for removal - **Won't remove!** In [October 2025 this FF](https://gitlab.com/gitlab-org/gitlab/-/issues/517914#note_2789831994) was turned into an [ops type](https://docs.gitlab.com/development/feature_flags/#ops-type) which are long-lived feature flags that control operational aspects of GitLab product behavior. Instead, the ownership should be forwarded - DRI @vanessaotto - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/225647
## Goal
- Check whether each feature flag is fully released
- Determine if feature flags can be safely removed
- Document reasons if they cannot be removed
- Simplify codebase by removing unnecessary flags
## TypeScript FF
**glql_typescript** is handled outside this work item and will be removed in https://gitlab.com/gitlab-org/gitlab/-/work_items/588881+
## Reference
Feature flags overview: https://samdbeckham.gitlab.io/feature-flags/#g=group%3A%3Aknowledge
issue