cleanup deprecation warnings about missing dyn with trait objects (#2997)

core/src/core/block.rs

@@ -123,7 +123,7 @@ pub struct HeaderEntry {
 }
 
 impl Readable for HeaderEntry {
-	fn read(reader: &mut Reader) -> Result<HeaderEntry, ser::Error> {
+	fn read(reader: &mut dyn Reader) -> Result<HeaderEntry, ser::Error> {
 		let hash = Hash::read(reader)?;
 		let timestamp = reader.read_u64()?;
 		let total_difficulty = Difficulty::read(reader)?;

core/src/core/pmmr/backend.rs

@@ -53,7 +53,7 @@ pub trait Backend<T: PMMRable> {
 	fn get_data_from_file(&self, position: u64) -> Option<T::E>;
 
 	/// Iterator over current (unpruned, unremoved) leaf positions.
-	fn leaf_pos_iter(&self) -> Box<Iterator<Item = u64> + '_>;
+	fn leaf_pos_iter(&self) -> Box<dyn Iterator<Item = u64> + '_>;
 
 	/// Remove Hash by insertion position. An index is also provided so the
 	/// underlying backend can implement some rollback of positions up to a

core/src/core/pmmr/rewindable_pmmr.rs

@@ -50,7 +50,7 @@ where
 	}
 
 	/// Reference to the underlying storage backend.
-	pub fn backend(&'a self) -> &Backend<T> {
+	pub fn backend(&'a self) -> &dyn Backend<T> {
 		self.backend
 	}