Remove hive-contrib jar from lib directory

As per HIVE-20020 hive-contrib jar is moved out of under Hive's lib. We 'export' some of our Hive dependencies into our lib folder too, and that includes hive-contrib.jar so in order to be synced with Hive we should remove it too.

We don't depend on this jar runtime so there's no use of it being in Pig's lib dir anyway.