Remove unused Gitaly feature flags

What does this MR do?

Remove stale data from the features table.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• [-] Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• Database guides
• [-] Separation of EE specific content

Performance and testing

The application does select the whole table in production. Less data to read is faster. I recon it's limited, but it still helps. Mostly listing the feature flags with chatops is less verbose after running this migration.