kiji-schema: SCHEMA-872. Deprecate KijiFirstKeyOnlyFilter

issue: https://jira.kiji.org/browse/SCHEMA-872
review: https://review.kiji.org/r/2041
commit: https://github.com/kijiproject/kiji-schema/commit/120ce7cb27f6acf4f84ff6ea6a56826d3033a88f