lint: use Keyify internally

[NathanBaulch]

There are 4 intersect helpers that could benefit from using the existing Keyify helper internally.

This is a question I have quite often whilst working on iterators support - when is it appropriate to use another helper and when is it better to implement from scratch?
There are lots of places where simple helpers like Empty or Map or even Ternary could be used. What about related helpers like like Count using CountBy internally, etc?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.45%. Comparing base (43cef1f) to head (0df8d7b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #691      +/-   ##
==========================================
- Coverage   94.48%   94.45%   -0.03%     
==========================================
  Files          18       18              
  Lines        3429     3411      -18     
==========================================
- Hits         3240     3222      -18     
  Misses        175      175              
  Partials       14       14              

Flag	Coverage Δ
unittests	94.45% <100.00%> (-0.03%)	⬇️

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[samber]

I'm pretty sure there is no difference in final asm code.

Go compiler inlines such methods when no side effect is detected.