Remove ZipSlices from benchmarks

[Philippe-Cholet]

ZipSlices was removed in 0.5.0.
Is there a point of keeping this around?!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.36%. Comparing base (6814180) to head (e859686).
Report is 44 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #911      +/-   ##
==========================================
- Coverage   94.38%   94.36%   -0.03%     
==========================================
  Files          48       48              
  Lines        6665     6815     +150     
==========================================
+ Hits         6291     6431     +140     
- Misses        374      384      +10     

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[jswrenn]

I can't see any reason we need to keep this around. Should the need arise for it, we can always add it back.