trie: remove Key in MissingNodeError

The key was constructed from nibbles, which isn't possible for all
nodes. Remove the only use of Key in LightTrie by always retrying with
the original key that was looked up.

trie/errors.go

@@ -30,10 +30,6 @@ import (
 //
 // RootHash is the original root of the trie that contains the node
 //
-// Key is a binary-encoded key that contains the prefix that leads to the first
-// missing node and optionally a suffix that hints on which further nodes should
-// also be retrieved
-//
 // PrefixLen is the nibble length of the key prefix that leads from the root to
 // the missing node
 //
@@ -42,7 +38,6 @@ import (
 // such hints in the error message)
 type MissingNodeError struct {
 	RootHash, NodeHash   common.Hash
-	Key                  []byte
 	PrefixLen, SuffixLen int
 }