qapi: Drop redundant flat-union-reverse-define test

qapi: Drop redundant flat-union-reverse-define test

As of commit 8c3f8e77, we test compilation of forward references
for a struct base type (UserDefOne), flat union base type
(UserDefUnionBase), and flat union branch type
(UserDefFlatUnion2). The only remaining forward reference being
tested for parsing in flat-union-reverse-define was a forward
enum declaration.  Once we make sure that always compiles,
the smaller parse-only test is redundant and can be deleted.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1444710158-8723-7-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>