[sglang, rollout] feat: delete remaining sglang spmd code

[PeterSH6]

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[gemini-code-assist]

Code Review

This pull request removes two files, verl/third_party/sglang/__init__.py and verl/third_party/sglang/parallel_state.py, to clean up what appears to be obsolete SPMD-related code for sglang. This is a straightforward code cleanup. After reviewing the provided repository context, I found no active usages of the deleted parallel_state.py module, which suggests this removal is safe and correct. The change is a good step towards simplifying the codebase.