### What this PR does / why we need it?
- This PR removes the Expert Parallel (EP) HCCL buffer allocation that
was previously introduced by the fused-op `dispatch_ffn_combine` (#3532
), since the fused-op has switch to MC2 HCCL buffer (#5156 ).
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: release/v0.13.0
- vLLM main:
ad32e3e19c
Signed-off-by: Chen Chen <0109chenchen@gmail.com>