Clean up duplicated code in lr_scheduler (#150984)

## Changes

- Remove duplicated code in `ReduceLROnPlateau`
- Remove redundant `noqa` comment

## Test Result

```bash
pytest test/optim/test_lrscheduler.py
```

![image](https://github.com/user-attachments/assets/37f91f31-0e77-4abf-9dd1-75538c0f0792)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/150984
Approved by: https://github.com/janeyx99

torch/optim/lr_scheduler.py

@@ -1214,15 +1214,7 @@ class ReduceLROnPlateau(LRScheduler):
             self.min_lrs = [min_lr] * len(optimizer.param_groups)
 
         self.patience = patience
-
         self.cooldown = cooldown
-        self.cooldown_counter = 0
-        self.mode = mode
-        self.threshold = threshold
-        self.threshold_mode = threshold_mode
-        self.best: float
-        self.num_bad_epochs: int
-        self.mode_worse: float  # the worse value for the chosen mode
         self.eps = eps
         self.last_epoch = 0
         self._last_lr = [group["lr"] for group in self.optimizer.param_groups]
@@ -1310,6 +1302,7 @@ class ReduceLROnPlateau(LRScheduler):
         if threshold_mode not in {"rel", "abs"}:
             raise ValueError("threshold mode " + threshold_mode + " is unknown!")
 
+        # the worse value for the chosen mode
         if mode == "min":
             self.mode_worse = inf
         else:  # mode == 'max':
@@ -1319,11 +1312,6 @@ class ReduceLROnPlateau(LRScheduler):
         self.threshold = threshold
         self.threshold_mode = threshold_mode
 
-    def state_dict(self):  # noqa: D102
-        return {
-            key: value for key, value in self.__dict__.items() if key != "optimizer"
-        }
-
     def load_state_dict(self, state_dict):
         """Load the scheduler's state."""
         self.__dict__.update(state_dict)
@@ -2007,7 +1995,7 @@ class OneCycleLR(LRScheduler):
 
         if step_num > self.total_steps:
             raise ValueError(
-                f"Tried to step {step_num} times. The specified number of total steps is {self.total_steps}"  # noqa: UP032
+                f"Tried to step {step_num} times. The specified number of total steps is {self.total_steps}"
             )
 
         for group in self.optimizer.param_groups: