MINOR: Remove spurious sleep in ConsumerCoordinatorTest

[showuon]

Follow up from here #12349 (comment)

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[showuon]

Fix for #12500

[showuon]

@ijuma @aiquestion , please take a look. Thanks.

Failed tests are unrelated:

    Build / JDK 8 and Scala 2.12 / org.apache.kafka.connect.mirror.integration.MirrorConnectorsIntegrationBaseTest.testReplicationWithEmptyPartition()
    Build / JDK 8 and Scala 2.12 / org.apache.kafka.controller.QuorumControllerTest.testBalancePartitionLeaders()
    Build / JDK 17 and Scala 2.13 / org.apache.kafka.controller.QuorumControllerTest.testSnapshotOnlyAfterConfiguredMinBytes()
    Build / JDK 17 and Scala 2.13 / org.apache.kafka.trogdor.coordinator.CoordinatorTest.testTaskRequestWithOldStartMsGetsUpdated()

[ijuma]

LGTM, thanks.