kiji-scoring: SCORE-140. Remove redundant metatable writes during freshener registration.

issue: https://jira.kiji.org/browse/SCORE-140
review: https://review.kiji.org/r/1427
commit: https://github.com/kijiproject/kiji-scoring/commit/f66d15f4344be7a1bb61ebca3e899698ab757ee8
kiji-scoring: SCORE-141. Properly cleanup freshness policies on unload from FreshKijiTableReader

issue: https://jira.kiji.org/browse/SCORE-141
review: https://review.kiji.org/r/1428
commit: https://github.com/kijiproject/kiji-scoring/commit/040c549caece9ce9e266fbb671845d819aeae8bb