accounts: remove UpdateAccount and last usages

Author: ellemouton

accounts/interface.go

@@ -207,11 +207,6 @@ type Store interface {
 		expirationDate time.Time, label string) (
 		*OffChainBalanceAccount, error)
 
-	// UpdateAccount writes an account to the database, overwriting the
-	// existing one if it exists.
-	UpdateAccount(ctx context.Context,
-		account *OffChainBalanceAccount) error
-
 	// Account retrieves an account from the Store and un-marshals it. If
 	// the account cannot be found, then ErrAccNotFound is returned.
 	Account(ctx context.Context, id AccountID) (*OffChainBalanceAccount,