Fix unused variables/parameters warnings

[seunghwak]

CUDA 11.4 reports additional warnings. Fix cuGraph warnings in this PR (still, there are many warnings coming from RAFT).

[codecov-commenter]

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@@               Coverage Diff               @@
##             branch-21.10    #1772   +/-   ##
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  Coverage                ?   59.63%           
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  Files                   ?       77           
  Lines                   ?     3535           
  Branches                ?        0           
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  Hits                    ?     2108           
  Misses                  ?     1427           
  Partials                ?        0           

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[seunghwak]

rerun tests

[BradReesWork]

@gpucibot merge