Obsoleted strings are treated as approved in Credits API

[SergeyBiryukov]

On the Credits page for 4.8 we have two contributors who don't appear to have any approved strings at any point (see the screenshots).

If I understand the process correctly:

• Contributor provides a suggestion.
• GTE neither approves nor rejects the suggestion, and makes their own translation instead.
• The original suggestion now has an old status, which is treated as "Approved, but obsoleted by another translation".

Strings that weren't explicitly approved shouldn't be counted in credits.

That said, the "Approved by:" line is only displayed for current strings, not for old or rejected later, so there's no way in the UI to check whether those strings were ever approved. If they were, this ticket is invalid, but GlotPress should provide a way to check that via the UI.