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/traits.rs

@@ -1,28 +0,0 @@
-pub type DBValue = Vec<u8>;
-
-#[derive(Debug)]
-pub struct DBError {
-    pub message: String,
-}
-
-impl DBError {
-    pub fn new(message: String) -> Self {
-        Self { message }
-    }
-}
-
-/// A generic database to be used by the "client' (i.e.,
-/// the lighthouse blockchain client).
-///
-/// The purpose of having this generic trait is to allow the
-/// program to use a persistent on-disk database during production,
-/// but use a transient database during tests.
-pub trait ClientDB: Sync + Send {
-    fn get(&self, col: &str, key: &[u8]) -> Result<Option<DBValue>, DBError>;
-
-    fn put(&self, col: &str, key: &[u8], val: &[u8]) -> Result<(), DBError>;
-
-    fn exists(&self, col: &str, key: &[u8]) -> Result<bool, DBError>;
-
-    fn delete(&self, col: &str, key: &[u8]) -> Result<(), DBError>;
-}