Better error handling for terminated or unsupported YouTube channels

[snappyapple632]

Checklist

• I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.
• This issue contains only one feature request. I will open one issue for every feature I want to request.

Describe the feature you want

Instead of a vague prompt showing that there was a problem loading terminated YouTube channels and a Guru Meditation error, show a proper error with an option to remove the terminated channel(s) from the subscription list.

Is your feature request related to a problem? Please describe it

NewPipe currently does not handle terminated channels very well, only showing a small prompt with a link to a Guru Meditation error.

Additional context

The error message that appears when you attempt to refresh a feed with a terminated or unsupported channel.

How will you/everyone benefit from this feature?

No more dreadful, menacing Guru Meditation errors for simply explained occurrences.

[triallax]

Thanks for opening an issue! I think this is a duplicate of #3313. If you disagree, feel free to write a comment.