Delete legacy renumbering implementation

[ChuckHastings]

This code is no longer used.

[codecov-commenter]

Codecov Report

Merging #1681 (91d219b) into branch-21.08 (1030a49) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 91d219b differs from pull request most recent head 3c26395. Consider uploading reports for the commit 3c26395 to get more accurate results

@@               Coverage Diff                @@
##           branch-21.08    #1681      +/-   ##
================================================
+ Coverage         59.77%   59.79%   +0.02%     
================================================
  Files                80       80              
  Lines              3540     3542       +2     
================================================
+ Hits               2116     2118       +2     
  Misses             1424     1424              

Impacted Files	Coverage Δ
python/cugraph/linear_assignment/lap.py	71.42% <100.00%> (ø)
python/cugraph/_version.py	44.80% <0.00%> (+0.39%)	⬆️

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[seunghwak]

Why's this breaking?

[ChuckHastings]

I labeled it breaking because it deletes a function from functions.hpp. Anyone that wrote code that depended on that function will break.

It was unclear to me which things that break outside users warrant that label. It doesn't break any python users... only if we have users of our legacy C++ API.

[Iroy30]

LGTM.

[BradReesWork]

@gpucibot merge