qapi: Drop unused error argument for list and implicit struct

No backend was setting an error when ending the visit of a list or
implicit struct, or when moving to the next list node.  Make the
callers a bit easier to follow by making this a part of the contract,
and removing the errp argument - callers can then unconditionally end
an object as part of cleanup without having to think about whether a
second error is dominated by a first, because there is no second
error.

A later patch will then tackle the larger task of splitting
visit_end_struct(), which can indeed set an error.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1454075341-13658-24-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/qapi/string-input-visitor.c b/qapi/string-input-visitor.c
index cdf129c..18b9339 100644
--- a/qapi/string-input-visitor.c
+++ b/qapi/string-input-visitor.c
@@ -1,7 +1,7 @@
 /*
  * String parsing visitor
  *
- * Copyright Red Hat, Inc. 2012
+ * Copyright Red Hat, Inc. 2012-2016
  *
  * Author: Paolo Bonzini <pbonzini@redhat.com>
  *
@@ -139,8 +139,7 @@
     }
 }
 
-static GenericList *
-next_list(Visitor *v, GenericList **list, Error **errp)
+static GenericList *next_list(Visitor *v, GenericList **list)
 {
     StringInputVisitor *siv = to_siv(v);
     GenericList **link;
@@ -178,8 +177,7 @@
     return *link;
 }
 
-static void
-end_list(Visitor *v, Error **errp)
+static void end_list(Visitor *v)
 {
     StringInputVisitor *siv = to_siv(v);
     siv->head = true;