Delete unused _setup.py #6353

Job	Run time
Build and Verify Docs	7m 31s
Build workflow from matrix	15s
Build MatX / Build MatX	4m 13s
Build RAPIDS / Check GH Event	4s
Build RAPIDS / rmm kvikio cudf cudf_kafka cuspatial	12m 1s
Build RAPIDS / rmm ucxx raft cuvs cumlprims_mg cuml	7m 44s
Build RAPIDS / rmm ucxx raft cugraph-ops cugraph cugraph-gnn	6m 38s
${{ matrix.name }}	0s
${{ matrix.name }}	0s
${{ matrix.name }}	0s
Verify Dev Containers / Verify devcontainer files are up-to-date	19s
cuda (python) CTK12.6 nvcc GCC / [GCC13] Test(amd64, V100)	46m 1s
Verify Dev Containers / ${{ matrix.devcontainer.name }}	0s
Build MatX / Notify Slack of MatX failure	0s
Build RAPIDS / Notify Slack of RAPIDS failure	0s
Verify and summarize workflow results	56s
CI	1s
	1h 25m 43s

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