removed not used imports, added doc
removed not used imports, added doc


Former-commit-id: 27e84393c782b6844708feeb753557448dd3eeaa [formerly ec08fee4904b17b2b47c047ad25adb8d247ff4cc]
Former-commit-id: 72dda83bf1f3a8360dd0c0995e7818edc96cc5db
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine