[GDN] remove XPU path of causal_conv1d_fn and causal_conv1d_update

[jiayisunx]

Motivation

Fix #34720.
There will be two backend for linear attention on XPU: triton and intel_xpu. Our plan:
For the triton backend, we always use triton kernels. That means we need to remove the standalong SYCL conv1d kernel from SGLang.
For the intel_xpu backend, we will use the fused SYCL GDN kernel (#33354)

Modifications

Remove the SYCL conv1d kernels and fallback to triton kernels.

Accuracy Tests

Speed Tests and Profiling

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.
• Follow the SGLang code style guidance.

Review and Merge Process

1. Ping Merge Oncalls to start the process. See the PR Merge Process.
2. Get approvals from CODEOWNERS and other reviewers.
3. Trigger CI tests with comments or contact authorized users to do so.
   • Common commands include /tag-and-rerun-ci, /tag-run-ci-label, /rerun-failed-ci
4. After green CI and required approvals, ask Merge Oncalls or people with Write permission to merge the PR.

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CI States

Latest PR Test (Base): ✅ Run #32438029441
Latest PR Test (Extra): ✅ Run #32703340685
Latest PR Test (AMD ROCm 7.2): ❌ Run #32438029391

[jiayisunx]

/tag-and-rerun-ci