### Apache Airflow version

2.4.2

### What happened

Hi all,

I would like to update the scheduler_job.py script by removing the unused attribute -> `self.using_mysql`.

I understand that `self.using_sqlite` attribute is used to define the variable `async_mode` in scheduler_job.py code, but noticed that `self.using_mysql` is not used.

You can check the code from [scheduler_job.py](https://github.com/apache/airflow/blob/main/airflow/jobs/scheduler_job.py),
```python
def __init__(...):
    # Check what SQL backend we use
    sql_conn: str = conf.get_mandatory_value('database', 'sql_alchemy_conn').lower()
    self.using_sqlite = sql_conn.startswith('sqlite')   # <- only self.using_sqlite is used for async_mode
    self.using_mysql = sql_conn.startswith('mysql')

...

def _execute(self) -> None:
    ...
    async_mode = not self.using_sqlite
```

not sure it was used before, but no longer used for the current scheduler.

If it's not the major change, would you mind me to remove it from the script?

Thanks in advance!

### What you think should happen instead

_No response_

### How to reproduce

_No response_

### Operating System

-

### Versions of Apache Airflow Providers

_No response_

### Deployment

Other

### Deployment details

_No response_

### Anything else

_No response_

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

#
#
#
from __future__ import annotations
import itertools
import logging
import multiprocessing
import os
import signal
import sys
import time
import warnings
from collections import defaultdict
from datetime import datetime, timedelta
from pathlib import Path
from typing import TYPE_CHECKING, Collection, DefaultDict, Iterator
from sqlalchemy import func, not_, or_, text
from sqlalchemy.exc import OperationalError
from sqlalchemy.orm import load_only, selectinload
from sqlalchemy.orm.session import Session, make_transient
from airflow import settings
from airflow.callbacks.callback_requests import DagCallbackRequest, SlaCallbackRequest, TaskCallbackRequest
from airflow.callbacks.pipe_callback_sink import PipeCallbackSink
from airflow.configuration import conf
from airflow.exceptions import RemovedInAirflow3Warning
from airflow.executors.executor_loader import UNPICKLEABLE_EXECUTORS
from airflow.jobs.base_job import BaseJob