[Feature flag] Cleanup license_scanning_sbom_scanner
<!-- Title suggestion: [Feature flag] Cleanup <feature-flag-name> -->
## Summary
This issue is to cleanup the `license_scanning_sbom_scanner` feature flag, after the feature flag has been enabled by default for an appropriate amount of time in production.
## Links
Feature flag rollout issue: https://gitlab.com/gitlab-org/gitlab/-/issues/385173
Main feature issue: https://gitlab.com/gitlab-org/gitlab/-/issues/384932+
Main doc issue: https://gitlab.com/gitlab-org/gitlab/-/issues/388439+
Release post: https://about.gitlab.com/releases/2023/02/22/gitlab-15-9-released/#new-license-compliance-scanner
Release post MR: https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/119232
## Owners
- Team: ~"group::composition analysis"
- Most appropriate slack channel to reach out to: `#g_secure-composition-analysis`
- Best individual to reach out to: @brytannia
- PM: @sam.white
## Stakeholders
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Are there any other stages or teams involved that need to be kept in the loop?
- Name of a PM
- The Support Team
- The Delivery Team
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## Expectations
### What might happen if this goes wrong?
<!-- Any MRs that need to be rolled back? Communication that needs to happen? What are some things you can think of that could go wrong - data loss or broken pages? -->
### Cleaning up the feature flag
<!-- The checklist here is to help stakeholders keep track of the feature flag status -->
- [x] Create a merge request to remove `<feature-flag-name>` feature flag. Ask for review and merge it.
- [x] Remove all references to the feature flag from the codebase.
- [x] Remove the YAML definitions for the feature from the repository.
- [x] Create [a changelog entry](https://docs.gitlab.com/ee/development/feature_flags/#changelog).
- [x] Ensure that the cleanup MR has been deployed to both production and canary.
If the merge request was deployed before [the code cutoff](https://about.gitlab.com/handbook/engineering/releases/#self-managed-releases-1),
the feature can be officially announced in a release blog post.
- [x] `/chatops run auto_deploy status <merge-commit-of-cleanup-mr>`
- [x] Close [the feature issue](ISSUE LINK) to indicate the feature will be released in the current milestone.
- [x] If not already done, clean up the feature flag from all environments by running these chatops command in `#production` channel:
- [x] `/chatops run feature delete <feature-flag-name> --dev`
- [x] `/chatops run feature delete <feature-flag-name> --staging`
- [x] `/chatops run feature delete <feature-flag-name>`
- [x] Close this rollout issue.
issue