Remove g_sequence_lookup from qemu-img help function

g_sequence_lookup is not supported by glib < 2.28. The usage
of g_sequence_lookup is not essential in this context (it's a
safeguard against duplicate values in the help message).
Removing the call enables the build on all platforms and
does not change the operation of the help function.

Signed-off-by: Mike Day <ncmike@ncultra.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/qemu-img.c b/qemu-img.c
index 04ce02a..1ad899e 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -70,11 +70,8 @@
 {
     GSequence *seq = opaque;
 
-    if (!g_sequence_lookup(seq, (gpointer)fmt_name,
-                           compare_data, NULL)) {
-        g_sequence_insert_sorted(seq, (gpointer)fmt_name,
-                                 compare_data, NULL);
-    }
+    g_sequence_insert_sorted(seq, (gpointer)fmt_name,
+                             compare_data, NULL);
 }
 
 static void QEMU_NORETURN GCC_FMT_ATTR(1, 2) error_exit(const char *fmt, ...)