Remove unused _is_known_via_attributes

[fingolfin]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.01%. Comparing base (bee81db) to head (8a34fe0).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2240   +/-   ##
=======================================
  Coverage   88.00%   88.01%           
=======================================
  Files         127      126    -1     
  Lines       31803    31800    -3     
=======================================
  Hits        27989    27989           
+ Misses       3814     3811    -3     

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[thofma]

Maybe in Oscar? Or maybe the plan was to use this in Oscar?

[fingolfin]

It is not used in any of our packages (I grepped for it), and as I recall it was meant as a kind of "demo" of what is possible but in the end we cut all uses of it, yet forgot to remove it itself.

Alas @HechtiDerLachs should comment as well

[HechtiDerLachs]

I'm fine with removing this. If one wanted to have this again, one can implement this for their custom types. But this generic fallback is not really needed. It must have been a demo at some point.