Move shuffling functions around

- Move `delegation` from the `transition` dir into its own dir:
`beacon_chain/validator_shuffling`
- Rename `beacon_chain/utils/shuffling` -> `vec_shuffle`

beacon_chain/validator_induction/src/lib.rs

@@ -10,3 +10,7 @@ pub use inductor::{
     ValidatorInductor,
     ValidatorInductionError,
 };
+
+pub use registration::{
+    ValidatorRegistration,
+};