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

eth2/state_processing/src/lib.rs

@@ -1,10 +0,0 @@
-mod block_processable;
-mod epoch_processable;
-mod slot_processable;
-
-pub use block_processable::{
-    validate_attestation, validate_attestation_without_signature, BlockProcessable,
-    Error as BlockProcessingError,
-};
-pub use epoch_processable::{EpochProcessable, Error as EpochProcessingError};
-pub use slot_processable::{Error as SlotProcessingError, SlotProcessable};