Strip out old code

All of these files have been moved to either:

- https://github.com/sigp/lighthouse-beacon
- https://github.com/sigp/lighthouse-validator
- https://github.com/sigp/lighthouse-common

For rationale, see: https://github.com/sigp/lighthouse/issues/197

beacon_node/db/src/lib.rs

@@ -1,14 +0,0 @@
-extern crate blake2_rfc as blake2;
-extern crate bls;
-extern crate rocksdb;
-
-mod disk_db;
-mod memory_db;
-pub mod stores;
-mod traits;
-
-use self::stores::COLUMNS;
-
-pub use self::disk_db::DiskDB;
-pub use self::memory_db::MemoryDB;
-pub use self::traits::{ClientDB, DBError, DBValue};