…no compressor found on transport layer, closes elastic#2076.

…no compressor found on transport layer, closes elastic#2076.

Removes a method that is no longer used in production code.

Relates to elastic#957

Removes a method that is no longer used in production code.

Relates to #957

* es/6.x: (155 commits)
  Make persistent tasks work. Made persistent tasks executors pluggable.
  Removed ClientHelper dependency from PersistentTasksService.
  Added AllocatedPersistentTask#waitForPersistentTaskStatus(...) that delegates to PersistentTasksService#waitForPersistentTaskStatus(...)
  Add adding ability to associate an ID with tasks.
  Remove InternalClient and InternalSecurityClient (#3054)
  Make the persistent task status available to PersistentTasksExecutor.nodeOperation(...) method
  Refactor/to x content fragments2 (#2329)
  Make AllocatedPersistentTask members volatile (#2297)
  Moves more classes over to ToXContentObject/Fragment (#2283)
  Adapt to upstream changes made to AbstractStreamableXContentTestCase (#2117)
  Move tribe to a module (#2088)
  Persistent Tasks: remove unused isCurrentStatus method (#2076)
  Call initialising constructor of BaseTasksRequest (#1771)
  Always Accumulate Transport Exceptions (#1619)
  Pass down the provided timeout.
  Fix static / version based BWC tests (#1456)
  Don't call ClusterService.state() in a ClusterStateUpdateTask
  Separate publishing from applying cluster states
  Persistent tasks: require allocation id on task completion (#1107)
  Fixes compile errors in Eclipse due to generics
  ...