distroseries.DistroSeriesView.checkTranslationsViewable should not raise exception from TAL

[Adi Roiban]

As discussed in this MP, distroseries.DistroSeriesView.checkTranslationsViewable() should not raise exception from TAL
https://code.edge.launchpad.net/~adiroiban/launchpad/bug-509252-take-2/+merge/19484

DistroSeriesView.checkTranslationsViewable() is used in a „metal” tag... so it really doesn't matter its return value as its sole purpose is to raise those exceptions.

<metal:check-available tal:omit-tag="view/checkTranslationsViewable" />

If we want to remove this behavior, we would need to raise those exception in Distribution URL traversal for series... and then things will get a bit complicated as those exception should be raised only for „translations” facet.