### What this PR does / why we need it?
reverts #5761 to fix accuracy issues when using piecewise graph mode.
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.13.0
- vLLM main:
2c24bc6996
Signed-off-by: Angazenn <supperccell@163.com>