[5min] Remove helper method and modernize

Previously, other extractor would go call a private(!) helper method. Instead, just hardcode the 5min:video_id format - it's not if that would ever change.
[streamcz] Update extractor
Fix imports and general cleanup

· Import from compat what comes from compat. Yes, some names are available in utils too, but that's an implementation detail.
· Use _match_id consistently whenever possible
· Fix some outdated tests
· Use consistent valid URL (always match the whole protocol, no ^ at start required)
· Use modern test definitions
[keek] Modernize and extract uploader