std.testing: delete refAllDeclsRecursive

suggested alternatives:
- actual tests
- explicitly list the decls
- compile an example application that uses the API
- stop worrying about dead code
- refAllDecls (non recursive) in each file

Don't fight the laziness, embrace it.

closes #23608
closes #30813
790d28d6cdAndrew Kelley committed on 1/16/2026, 8:34:42 PMparent0818882
3 files changedLine totals unavailable