kiji-express: EXP-302. Remove references to KijiSlice from kiji-express.

issue: https://jira.kiji.org/browse/EXP-302
review: https://review.kiji.org/r/1368
commit: https://github.com/kijiproject/kiji-express/commit/571dd7bd65128e20e2715c17fc43680cafbef174