Revert "Switch to fixed version of Play for Play2-SBT-Plugin."

This reverts commit 367fd59cb7da4bad831d27584b9d19c3893a492d.

The root cause for workaround in 367fd59cb7da4bad831d27584b9d19c3893a492d
has been fixed upstream in playframework/playframework#3736. We can revert
the workaround now.