Enable grumpkin-msm CUDA feature (microsoft#279)

* chore: Refactor CUDA feature dependencies in Cargo.toml

- Removed unused neptune cuda feature in the project's `Cargo.toml`

Closes microsoft#275

* Enable `grumpkin-msm` CUDA feature

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Co-authored-by: François Garillot <francois@garillot.net>

Cargo.toml

@@ -111,7 +111,7 @@ abomonate = []
 asm = ["halo2curves/asm"]
 # Compiles in portable mode, w/o ISA extensions => binary can be executed on all systems.
 portable = ["grumpkin-msm/portable"]
-cuda = ["neptune/cuda", "neptune/pasta", "neptune/arity24"]
+cuda = ["grumpkin-msm/cuda"]
 flamegraph = ["pprof/flamegraph", "pprof/criterion"]
 
 # This is needed to ensure halo2curves, which imports pasta-curves, uses the *same* traits in bn256_grumpkin