remove unused StorableAccounts (solana-labs#956)

accounts-db/src/storable_accounts.rs

@@ -153,25 +153,7 @@ impl<'a: 'b, 'b> StorableAccounts<'a> for (Slot, &'b [(&'a Pubkey, &'a AccountSh
         self.1.len()
     }
 }
-impl<'a> StorableAccounts<'a> for (Slot, &'a [&'a StoredAccountMeta<'a>]) {
-    fn account<Ret>(
-        &self,
-        index: usize,
-        mut callback: impl for<'local> FnMut(AccountForStorage<'local>) -> Ret,
-    ) -> Ret {
-        callback(self.1[index].into())
-    }
-    fn slot(&self, _index: usize) -> Slot {
-        // per-index slot is not unique per slot when per-account slot is not included in the source data
-        self.0
-    }
-    fn target_slot(&self) -> Slot {
-        self.0
-    }
-    fn len(&self) -> usize {
-        self.1.len()
-    }
-}
+
 /// holds slices of accounts being moved FROM a common source slot to 'target_slot'
 pub struct StorableAccountsBySlot<'a> {
     target_slot: Slot,
@@ -274,6 +256,27 @@ pub mod tests {
         },
     };
 
+    /// this is no longer used. It is very tricky to get these right. There are already tests for this. It is likely worth it to leave this here for a while until everything has settled.
+    impl<'a> StorableAccounts<'a> for (Slot, &'a [&'a StoredAccountMeta<'a>]) {
+        fn account<Ret>(
+            &self,
+            index: usize,
+            mut callback: impl for<'local> FnMut(AccountForStorage<'local>) -> Ret,
+        ) -> Ret {
+            callback(self.1[index].into())
+        }
+        fn slot(&self, _index: usize) -> Slot {
+            // per-index slot is not unique per slot when per-account slot is not included in the source data
+            self.0
+        }
+        fn target_slot(&self) -> Slot {
+            self.0
+        }
+        fn len(&self) -> usize {
+            self.1.len()
+        }
+    }
+
     /// this is no longer used. It is very tricky to get these right. There are already tests for this. It is likely worth it to leave this here for a while until everything has settled.
     impl<'a, T: ReadableAccount + Sync> StorableAccounts<'a> for (Slot, &'a [&'a (Pubkey, T)])
     where