Remove critical error for vinyl tracknumber tags

[MacroPower]

        tracknumber = info['tracknumber'][0]
        if not valid_fractional_tag(tracknumber):
            return (False, '"%s" has a malformed tracknumber tag ("%s")' % (filename, tracknumber))

We currently have this block dictating what is "acceptable" for tracknumber tags.

However, it does not account for vinyl releases. It has been long upheld that A1, B7, etc are acceptable tracknumber tags.

Perhaps this could be changed to simply be an info message, or be refined to allow tags such as "A1" or "C6/20".

In the very least we could have an option to ignore the error.