Refactor cugraph RMAT to use PLC RMAT

[rlratzel]

Who: cugraph developers
What: update cugraph RMAT to remove the legacy cython wrapper and call PLC RMAT directly
Why: This allows the cugraph team to remove tech debt by removing the cython.cu file completely. This also makes RMAT consistent with the other APIs that call PLC APIs directly instead of binding to libcugraph C++ directly (PLC is intended to be the layer which binds to libcugraph directly)

Tasks

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1. Add RMAT generation to PLC #2817
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2. Modify Python to call PLC version of RMAT generation #2818
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3. Remove RMAT generation from cython.cu #2820
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4. update C API to add functionality in RMAT cython.cu code #3670
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