Use matches!(..) to make TrieNode::is_empty more concise

cranelift/isle/isle/src/codegen.rs

@@ -234,10 +234,7 @@ enum TrieNode {
 
 impl TrieNode {
     fn is_empty(&self) -> bool {
-        match self {
+        matches!(self, &TrieNode::Empty)
-            &TrieNode::Empty => true,
-            _ => false,
-        }
     }
 
     fn insert(