Depends how you are doing this. Generally, this may get you into hot water with CASL. If you are letting Sales people send the email by itself, might be ok. If you are sending 10,000 emails on behalf of Lead Owner, you better leave that link in there.
1. Admin > Sales Insight lets you do this if the email is sent via sales insight.
2. Adjust templates - remove the default Admin > Email > Unsubscribe text and only put it in email templates that you want to use it in. For sales emails, leave it out.