[Core] Comment out unused code in sampler

[peng1999]

The sampling_seeds, sample_indices, and extra_seeds member in SamplingTensors is only for triton sampler, which is incomplete and currently stalled in development (See #3186, #3626). This PR comments out some related code. This will eliminate the call to _get_sequence_seeds, which consists ~17% in the construction of SamplingTensors in my profiling.

If maintainers decide not to continue developing triton sampler in the near future, I recommend removing the fields mentioned above from SamplingTensors to make code cleaner and improve performance.

cc @Yard1

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[peng1999]

This change is to avoid pytorch warning because sampling_seeds_t becomes 1-dim here.

[Yard1]

The triton sampler is pending changes to triton which will reduce kernel launch overhead. The construction of sampling seems should be overlapped with GPU forward pass if using cuda graphs making it essentially free (the overhead is hidden). That being said, we can comment this out for now and add it back in the future when the kernel is enabled.

[youkaichao]

Can we directly remove the relevant code? We can add it back later if necessary.

Commenting the code in the codebase sounds not good to me.

[Yard1]

I'd suggest we gate it behind a global flag hardcoded to false for now. I will take a look at the triton sampler again once we update to torch 2.4 & triton 3.0.0

[youkaichao]

LGTM, @peng1999 can you make a hard-coded False flag, and guard these fields under the flag?

[peng1999]

Changed to hard-coded False flag as per comments.

[youkaichao]

Thanks for the great fix!

[youkaichao]

we can force merge if only tracing related tests fail, which are already fixed in main via #7065 and can be ignored.