RMAN-08137: WARNING: archive log not deleted as it is still needed

Use following command at your own risk , because it deletes all your archivelog by ignoring the retention period  or without caring that they have been applied on STANDBY database or not.

If you use the DELETE command with the optional FORCE keyword, RMAN deletes the specified backups, but ignores any I/O errors, including those that occur when a backup is missing from disk or tape. It then updates the RMAN repository to reflect the fact that the backup is deleted, regardless of whether RMAN was able to delete the file or whether the file was already missing. For example:

rman > delete force noprompt archivelog all completed before 'sysdate -7';

another e.g. DELETE FORCE NOPROMPT BACKUPSET TAG 'weekly_bkup';