Move all attestaion fns into same file

eth2/types/src/attestation.rs

@@ -5,8 +5,6 @@ use rand::RngCore;
 use serde_derive::Serialize;
 use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 
-mod signing;
-
 #[derive(Debug, Clone, PartialEq, Serialize)]
 pub struct Attestation {
     pub data: AttestationData,
@@ -19,6 +17,10 @@ impl Attestation {
     pub fn canonical_root(&self) -> Hash256 {
         Hash256::from(&self.hash_tree_root()[..])
     }
+
+    pub fn signable_message(&self, custody_bit: bool) -> Vec<u8> {
+        self.data.signable_message(custody_bit)
+    }
 }
 
 impl Encodable for Attestation {

eth2/types/src/attestation/signing.rs

@@ -1,7 +0,0 @@
-use crate::Attestation;
-
-impl Attestation {
-    pub fn signable_message(&self, custody_bit: bool) -> Vec<u8> {
-        self.data.signable_message(custody_bit)
-    }
-}