MINOR: Removed unused local variable in method DefaultStateUpdater.drainRestoredActiveTasks

[kumarlokesh]

The value of the local variable elapsed is not used within the
method drainRestoredActiveTasks.

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[mjsax]

LGTM, assuming build passes

[mjsax]

@kumarlokesh -- build failed with a spotbug error. Can you take a look and fix.