Fixing flaky test JSONSerializerTest2.test_0

[OrDTesters]

test_0 in JSONSerializerTest2 has a test-order dependency and it fails when it is run after JSONSerializerTest2.test_3.

test_0 can be fixed by clearing the serializers. The fix will enable test_0 to now pass in any test run order. Without the fix, the tests will get the following error. Let me know if you want to discuss more.

java.lang.AssertionError
	at org.junit.Assert.fail(Assert.java:86)
	at org.junit.Assert.assertTrue(Assert.java:41)
	at org.junit.Assert.assertTrue(Assert.java:52)
	at com.alibaba.json.bvt.serializer.JSONSerializerTest2.test_0(JSONSerializerTest2.java:24)

[CLAassistant]

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