Creating sub-tries now never hashes leaves

- Plonky2 expects (not sure if it's always) leaves to never be hashed
  that it traverses down to, even if there isn't a read/write on the
  leaf itself. Note however that it is fine to hash any nodes above the
  leaf

mpt_trie/src/trie_subsets.rs

@@ -316,10 +316,7 @@ fn mark_nodes_that_are_needed<N: PartialTrie>(
             }
         }
         TrackedNodeIntern::Leaf => {
-            let (k, _) = trie.info.get_leaf_nibbles_and_value_expected();
-            if k == curr_nibbles {
-                trie.info.touched = true;
-            }
+            trie.info.touched = true;
         }
     }