Do not alert if port is conflicted by another Scratch Link

[terado0618]

Proposed Changes

Scratch Link does not show alert dialog about port conflict if the port is used by another Scratch Link.

Reason for Changes

On our workshops with Scratch 3.0 and Scratch Link, some attendees were surprised at an alert dialog which looks like a serious problem, especially for beginners who do not understand technical terms or English.

If the port is used by another Scratch Link, it is actually ready to use and there is no required intention or operation from the user, except another Scratch Link is old version.
So, for better user experience, I hope that Scratch Link is silently terminated in this case.