Remove unused imports

[ttim]

Remove unused imports across summingbird project.

[codecov-io]

Codecov Report

Merging #718 into develop will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #718   +/-   ##
========================================
  Coverage    70.88%   70.88%           
========================================
  Files          141      141           
  Lines         3479     3479           
  Branches       202      202           
========================================
  Hits          2466     2466           
  Misses        1013     1013

Impacted Files	Coverage Δ
...la/com/twitter/summingbird/scalding/TestUtil.scala	49.12% <ø> (ø)	:white_check_mark:
...ingbird/scalding/service/SimpleWindowService.scala	0% <ø> (ø)	:white_check_mark:
...cala/com/twitter/summingbird/example/Storage.scala	76.47% <ø> (ø)	:white_check_mark:
...a/com/twitter/summingbird/example/ExampleJob.scala	0% <ø> (ø)	:white_check_mark:
...twitter/summingbird/builder/CompletedBuilder.scala	100% <ø> (ø)	:white_check_mark:
...scala/com/twitter/summingbird/storm/Executor.scala	0% <ø> (ø)	:white_check_mark:
...om/twitter/summingbird/scalding/MockMappable.scala	91.66% <ø> (ø)	:white_check_mark:
...om/twitter/summingbird/builder/SourceBuilder.scala	46.15% <ø> (ø)	:white_check_mark:
...a/com/twitter/summingbird/storm/StormTestRun.scala	79.41% <ø> (ø)	:white_check_mark:
...om/twitter/summingbird/store/MergeOperations.scala	100% <ø> (ø)	:white_check_mark:
... and 41 more

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[johnynek]

👍 this is really great!