container: viewDB.withTxn: don't wrap errors

The withTxn function takes a custom function to execute; we should not
wrap those errors as the only responsibility of this function is to
execute the given function in a transaction.

This was introduced in 6549a270e9, and
an oversight of me.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

container/view.go

@@ -152,7 +152,7 @@ func (db *ViewDB) withTxn(cb func(*memdb.Txn) error) error {
 	err := cb(txn)
 	if err != nil {
 		txn.Abort()
-		return errdefs.System(err)
+		return err
 	}
 	txn.Commit()
 	return nil