Simplify prometheus metrics (#1981)

Co-authored-by: Mohit Reddy <mohitreddy1996@users.noreply.github.com>

python/sglang/srt/managers/schedule_batch.py

@@ -31,7 +31,6 @@ ScheduleBatch -> ModelWorkerBatch -> ForwardBatch
 
 import dataclasses
 import logging
-import time
 from typing import List, Optional, Tuple, Union
 
 import torch
@@ -255,16 +254,6 @@ class Req:
         # For Qwen2-VL
         self.mrope_position_delta = []  # use mutable object
 
-        # Lifetime traces
-        # time when request is created and added to waitlist
-        self.created_time = None
-        # time when request is added to prefill batch
-        self.queued_time = None
-        # time when request is being processed
-        self.started_time = None
-        # time when request is finished
-        self.finished_time = None
-
     # whether request reached finished condition
     def finished(self) -> bool:
         return self.finished_reason is not None
@@ -1038,10 +1027,6 @@ class ScheduleBatch:
             f"#req={(len(self.reqs))})"
         )
 
-    def mark_reqs_started(self):
-        for req in self.reqs:
-            req.started_time = time.time()
-
 
 @dataclasses.dataclass
 class ModelWorkerBatch: