Use mem::take instead of mem::replace where appropriate (#5846)

* replace replace with take

* Update client/api/src/cht.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update client/api/src/cht.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/utils/fork-tree/src/lib.rs

@@ -114,7 +114,7 @@ impl<H, N, V> ForkTree<H, N, V> where
 		)?;
 
 		let removed = if let Some(mut root_index) = new_root_index {
-			let mut old_roots = std::mem::replace(&mut self.roots, Vec::new());
+			let mut old_roots = std::mem::take(&mut self.roots);
 
 			let mut root = None;
 			let mut cur_children = Some(&mut old_roots);
@@ -137,7 +137,7 @@ impl<H, N, V> ForkTree<H, N, V> where
 
 			// we found the deepest ancestor of the finalized block, so we prune
 			// out any children that don't include the finalized block.
-			let root_children = std::mem::replace(&mut root.children, Vec::new());
+			let root_children = std::mem::take(&mut root.children);
 			let mut is_first = true;
 
 			for child in root_children {