[SPARK-33810][TESTS] Reenable test cases disabled in SPARK-31732

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

The test failures were due to machine being slow in Jenkins. We switched to Ubuntu 20 if I am not wrong.
Looks like all machines are functioning properly unlike the past, and the tests pass without a problem anymore.

This PR proposes to enable them back.

### Why are the changes needed?

To restore test coverage.

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

No, dev-only.

### How was this patch tested?

Jenkins jobs in this PR show the flakiness.

Closes #30798 from HyukjinKwon/do-not-merge-test.

Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

Author: HyukjinKwon

external/kafka-0-10-sql/src/test/scala/org/apache/spark/sql/kafka010/KafkaMicroBatchSourceSuite.scala

@@ -349,8 +349,7 @@ abstract class KafkaMicroBatchSourceSuiteBase extends KafkaSourceSuiteBase {
     )
   }
 
-  // TODO (SPARK-31731): re-enable it
-  ignore("subscribing topic by pattern with topic deletions") {
+  test("subscribing topic by pattern with topic deletions") {
     val topicPrefix = newTopic()
     val topic = topicPrefix + "-seems"
     val topic2 = topicPrefix + "-bad"

external/kafka-0-10-sql/src/test/scala/org/apache/spark/sql/kafka010/KafkaRelationSuite.scala

@@ -174,8 +174,7 @@ abstract class KafkaRelationSuiteBase extends QueryTest with SharedSparkSession
       ("3", Seq(("e", "f".getBytes(UTF_8)), ("e", "g".getBytes(UTF_8))))).toDF)
   }
 
-  // TODO (SPARK-31729): re-enable it
-  ignore("timestamp provided for starting and ending") {
+  test("timestamp provided for starting and ending") {
     val (topic, timestamps) = prepareTimestampRelatedUnitTest
 
     // timestamp both presented: starting "first" ending "finalized"

external/kafka-0-10/src/test/scala/org/apache/spark/streaming/kafka010/DirectKafkaStreamSuite.scala

@@ -332,8 +332,7 @@ class DirectKafkaStreamSuite
   }
 
   // Test to verify the offset ranges can be recovered from the checkpoints
-  // TODO (SPARK-31722): re-enable it
-  ignore("offset recovery") {
+  test("offset recovery") {
     val topic = "recovery"
     kafkaTestUtils.createTopic(topic)
     testDir = Utils.createTempDir()
@@ -420,8 +419,7 @@ class DirectKafkaStreamSuite
   }
 
   // Test to verify the offsets can be recovered from Kafka
-  // TODO (SPARK-31722): re-enable it
-  ignore("offset recovery from kafka") {
+  test("offset recovery from kafka") {
     val topic = "recoveryfromkafka"
     kafkaTestUtils.createTopic(topic)
 

streaming/src/test/scala/org/apache/spark/streaming/StreamingContextSuite.scala

@@ -293,8 +293,7 @@ class StreamingContextSuite
     }
   }
 
-  // TODO (SPARK-31728): re-enable it
-  ignore("stop gracefully") {
+  test("stop gracefully") {
     val conf = new SparkConf().setMaster(master).setAppName(appName)
     conf.set("spark.dummyTimeConfig", "3600s")
     val sc = new SparkContext(conf)