[Streaming][Minor] Remove useless type signature of Java Kafka direct stream API

[jerryshao]

cc @tdas .

[SparkQA]

Test build #28082 has started for PR 4817 at commit eebfaac.

• This patch merges cleanly.

[SparkQA]

Test build #28082 has finished for PR 4817 at commit eebfaac.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • logError("User class threw exception: " + cause.getMessage, cause)

[AmplabJenkins]

Test PASSed.
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Test PASSed.

[tdas]

Very good catch!! It is called from Java unit tests, I am not sure how we did not catch this. Maybe because I dont explicitly specify the generic params.

I am merging this to make sure this gets into Spark 1.3 RC2, but could you make another PR to fix the Java unit tests (specify types) so that such issues get caught?