Do not warn changelog required when removing feature flag patches

What does this MR do and why?

Do not warn changelog required when removing feature flag patches

Danger checks if we are removing feature flag files without a changelog entry and reports:

This merge request requires a changelog entry because it [removes a feature flag](https://docs.gitlab.com/ee/development/changelog.html#what-warrants-a-changelog-entry).

This happens inside the gitlab-dangerfiles

As far as I can tell we only use the feature flag category in danger for this specific check so we don't need to recategorize the patch files.

Fixes #506518 (closed)

Changelog: fixed

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