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/beacon_chain/src/lib.rs

@@ -1,9 +0,0 @@
-mod attestation_aggregator;
-mod attestation_targets;
-mod beacon_chain;
-mod block_graph;
-mod checkpoint;
-mod lmd_ghost;
-
-pub use self::beacon_chain::{BeaconChain, Error};
-pub use self::checkpoint::CheckPoint;