[SPARK-30530][SQL][FOLLOW-UP] Remove unnecessary codes and fix comments accordingly in UnivocityParser

[HyukjinKwon]

What changes were proposed in this pull request?

This PR proposes to clean up UnivocityParser.

Why are the changes needed?

It will slightly improve the performance since we don't do unnecessary computation for Array concatenations/creation.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

Manually ran the existing tests.

[HyukjinKwon]

cc @cloud-fan and @MaxGekk. It's rather minor but wanted to clean up here.

[SparkQA]

Test build #117081 has finished for PR 27287 at commit e2cf12a.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #117087 has finished for PR 27287 at commit c2c5ab0.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #117077 has finished for PR 27287 at commit bde0b64.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

retest this please

[HyukjinKwon]

retest this please

[MaxGekk]

Something wrong is going on in #27287 (comment). This exception shouldn't happen:

Caused by: java.lang.IllegalStateException: Number of logging event reached the limit: 100
	at org.apache.spark.SparkFunSuite$LogAppender.append(SparkFunSuite.scala:197)
	at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:251)

It was added by #27166, and the limit shouldn't be reachable.

The test doesn't register any log appenders:

spark/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/csv/CSVSuite.scala

Lines 1731 to 1761 in d4c6ec6

	test("SPARK-23786: enforce inferred schema") {
	val expectedSchema = new StructType().add("_c0", DoubleType).add("_c1", StringType)
	val withHeader = spark.read
	.option("inferSchema", true)
	.option("enforceSchema", false)
	.option("header", true)
	.csv(Seq("_c0,_c1", "1.0,a").toDS())
	assert(withHeader.schema == expectedSchema)
	checkAnswer(withHeader, Seq(Row(1.0, "a")))
	// Ignore the inferSchema flag if an user sets a schema
	val schema = new StructType().add("colA", DoubleType).add("colB", StringType)
	val ds = spark.read
	.option("inferSchema", true)
	.option("enforceSchema", false)
	.option("header", true)
	.schema(schema)
	.csv(Seq("colA,colB", "1.0,a").toDS())
	assert(ds.schema == schema)
	checkAnswer(ds, Seq(Row(1.0, "a")))
	val exception = intercept[IllegalArgumentException] {
	spark.read
	.option("inferSchema", true)
	.option("enforceSchema", false)
	.option("header", true)
	.schema(schema)
	.csv(Seq("col1,col2", "1.0,a").toDS())
	}
	assert(exception.getMessage.contains("CSV header does not conform to the schema"))
	}

but some appender throws exceptions.

[MaxGekk]

I propose to assign names to log appenders, and print the names in exception. So, we will know which one wasn't removed.

[SparkQA]

Test build #117097 has finished for PR 27287 at commit c2c5ab0.

• This patch fails from timeout after a configured wait of 400m.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Jenkins, retest this please

[SparkQA]

Test build #117121 has finished for PR 27287 at commit c2c5ab0.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #117124 has finished for PR 27287 at commit c2c5ab0.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

Merged to master.