Invitation links show registration step when registration link is disabled

Description:

Currently, the registration link is disabled and it's available only via OAuth provider.

Via the normal login page https://chat.example.com it's not showing as expected, but when I send an invitation link to someone it appears.

Steps to reproduce:

1. Add an OAuth provider
2. Disable all the other authentication/registration methods
3. Send an invitation link to someone

Expected behavior:

To see the login via oauth provider only, like the main login page:

Actual behavior:

I'm seeing the login and a registration link right below:

Server Setup Information:

• Version of Rocket.Chat Server: 3.5.4
• Operating System: Ubuntu 20.04
• Deployment Method: docker-compose
• Number of Running Instances: 1
• DB Replicaset Oplog: Enabled
• NodeJS Version: v12.16.1
• MongoDB Version: 4.0.20

Client Setup Information

• Desktop App or Browser Version: Google Chrome | 84.0.4147.135 (Official Build) (64-bit)
• Operating System: Mac OS 10.15.6