Make RealmDistinctableField interface and implementers deprecated

[JamesDurham]

distinct(String!): RealmResults! is deprecated. Deprecated in Java

distinct(String!, vararg String!): RealmResults! is deprecated. Deprecated in Java

[PaulDGillis]

Should be distinctValues since distinct now returns RealmQuery instead of RealmResults. Edit: Should be fixed since in the latest release of realm distinctValues is now distinct