Remove unnecessary rule for hvcat_fill!

[yuyichao]

The new version in base should be type stable now.

It might be better to change the test to test the higher level function that uses hvcat_fill! but I'm still working on other changes to make it run on master.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.99%. Comparing base (70af14d) to head (0eb9ee1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3490       +/-   ##
===========================================
+ Coverage   44.21%   76.99%   +32.77%     
===========================================
  Files          55       68       +13     
  Lines       21509    22668     +1159     
===========================================
+ Hits         9511    17454     +7943     
+ Misses      11998     5214     -6784     

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