[REVIEW] Remove gdf_column from db

[jwyles]

This PR removes the use of gdf_column from the db code. It also re-enables find_matches tests which were previously failing in CI to see if they still fail now.

[afender]

looks good to me

[BradReesWork]

rerun tests

[BradReesWork]

@jwyles Test_FindMatches.fifthTest is failing

[codecov-io]

Codecov Report

Merging #802 into branch-0.14 will decrease coverage by 0.21%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.14     #802      +/-   ##
===============================================
- Coverage        58.14%   57.93%   -0.22%     
===============================================
  Files               44       44              
  Lines             1264     1248      -16     
===============================================
- Hits               735      723      -12     
+ Misses             529      525       -4     

Impacted Files	Coverage Δ
python/cugraph/structure/graph.py	69.72% <0.00%> (-0.37%)	⬇️
python/cugraph/community/ecg.py	100.00% <0.00%> (ø)
python/cugraph/traversal/bfs.py	100.00% <0.00%> (ø)
python/cugraph/traversal/sssp.py	73.33% <0.00%> (ø)
python/cugraph/community/louvain.py	85.71% <0.00%> (ø)
python/cugraph/cores/core_number.py	100.00% <0.00%> (ø)
python/cugraph/cores/ktruss_subgraph.py	100.00% <0.00%> (ø)
python/cugraph/link_analysis/pagerank.py	100.00% <0.00%> (ø)
python/cugraph/link_prediction/jaccard.py	86.66% <0.00%> (ø)
python/cugraph/link_prediction/overlap.py	75.00% <0.00%> (ø)
... and 6 more

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