for me you're taking a useless risk with a table with so many records.
Since this column is not used, it doesn't contain data so it doesn't consume space.
If anything goes wrong for this single column cleaning it would take lots of efforts to bring back a clean situation with anyway this column.
You should re-assess the need/relevance of dropping this column.
For any DB activity for which you don't feel comfortable you need to
- stop your system
- take a backup
- execute your DB activities
- perform sanity at DB level
- start your apps with no/minimum processing
- enable your business when it looks OK
ideally, put a prod backup on a test system and execute a full rehearsal of your procedure.