fix prunning: use correct state root and don't require account address

[magicxyyz]

This PR:

• uses block root as state root in trie.StorageTrieID call (previously leaf key was passed)
  

  go-ethereum/trie/trie_id.go

  Lines 22 to 26 in b1622e6

  	type ID struct {
  	StateRoot common.Hash // The root of the corresponding state(block.root)
  	Owner common.Hash // The contract address hash which the trie belongs to
  	Root common.Hash // The root hash of trie
  	}

  
  

  go-ethereum/trie/trie_id.go

  Lines 37 to 45 in b1622e6

  	// StorageTrieID constructs an identifier for storage trie which belongs to a certain
  	// state and contract specified by the stateRoot and owner.
  	func StorageTrieID(stateRoot common.Hash, owner common.Hash, root common.Hash) *ID {
  	return &ID{
  	StateRoot: stateRoot,
  	Owner: owner,
  	Root: root,
  	}
  	}

• similarly to upstream, uses trie.NewStateTrie directly instead of OpenStorageTrie to not require preimage of account address hash

[PlasmaPower]

LGTM