Remove dev feature flag from POST /discord-actions/nicknames/sync API

[samarpan1738]

Issue Description

This API has been live on prod for a long time but the feature flag has not been removed.
Remove the dev FF from backend and all other repos where its being used

Usages in other repos

1. website-dashboard - All usages are using dev feature flag ✅
2. cron-jobs - All usages are using dev feature flag ✅

This is a subtask of #2075

Expected Behavior

Current Behavior

Screenshots

NA

Reproducibility

• This issue is reproducible
• This issue is not reproducible

Steps to Reproduce

NA

Severity/Priority

• Critical
• High
• Medium
• Low

Additional Information

Checklist

• I have read and followed the project's code of conduct.
• I have searched for similar issues before creating this one.
• I have provided all the necessary information to understand and reproduce the issue.
• I am willing to contribute to the resolution of this issue.