[SPARK-39273][PS][TESTS] Make PandasOnSparkTestCase inherit ReusedSQLTestCase

### What changes were proposed in this pull request?

This PR proposes to make `PandasOnSparkTestCase` inherit `ReusedSQLTestCase`.

### Why are the changes needed?

We don't need this:

```python
    classmethod
    def tearDownClass(cls):
        # We don't stop Spark session to reuse across all tests.
        # The Spark session will be started and stopped at PyTest session level.
        # Please see pyspark/pandas/conftest.py.
        pass
```

anymore in Apache Spark. This has existed to speed up the tests when the codes are in Koalas repository where the tests run sequentially in single process.

In Apache Spark, we run in multiple processes, and we don't need this anymore.

### Does this PR introduce _any_ user-facing change?

No, test-only.

### How was this patch tested?

Existing CI should test it out.

Closes apache#36652 from HyukjinKwon/SPARK-39273.

Authored-by: Hyukjin Kwon <gurwls223@apache.org>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

Author: HyukjinKwon

python/pyspark/testing/pandasutils.py

@@ -18,7 +18,6 @@
 import functools
 import shutil
 import tempfile
-import unittest
 import warnings
 from contextlib import contextmanager
 from distutils.version import LooseVersion
@@ -32,9 +31,8 @@
 from pyspark.pandas.frame import DataFrame
 from pyspark.pandas.indexes import Index
 from pyspark.pandas.series import Series
-from pyspark.pandas.utils import default_session, SPARK_CONF_ARROW_ENABLED
-from pyspark.testing.sqlutils import SQLTestUtils
-
+from pyspark.pandas.utils import SPARK_CONF_ARROW_ENABLED
+from pyspark.testing.sqlutils import ReusedSQLTestCase
 
 tabulate_requirement_message = None
 try:
@@ -61,19 +59,12 @@
 have_plotly = plotly_requirement_message is None
 
 
-class PandasOnSparkTestCase(unittest.TestCase, SQLTestUtils):
+class PandasOnSparkTestCase(ReusedSQLTestCase):
     @classmethod
     def setUpClass(cls):
-        cls.spark = default_session()
+        super(PandasOnSparkTestCase, cls).setUpClass()
         cls.spark.conf.set(SPARK_CONF_ARROW_ENABLED, True)
 
-    @classmethod
-    def tearDownClass(cls):
-        # We don't stop Spark session to reuse across all tests.
-        # The Spark session will be started and stopped at PyTest session level.
-        # Please see pyspark/pandas/conftest.py.
-        pass
-
     def assertPandasEqual(self, left, right, check_exact=True):
         if isinstance(left, pd.DataFrame) and isinstance(right, pd.DataFrame):
             try: