To Remove "Create account" or "Don't have an account?"from the login form 

If you don't want users to register from the front end, or you want only the managed users to login your site. you just need to follow the steps below to disable the registration.

1. Log into the backend (administrator area)

2. Click on “User Manager” > Options (Icon on the top right) > Component > Allow User Registration > SELECT “No”

3. Save

Now when you go to your frontend you will see that the field"Create account" or "Don't have an account?" has been removed. You can still add users from the backend.