qmp: Clean up qmp_query_spice() #ifndef !CONFIG_SPICE dummy

QMP command query-spice exists only #ifdef CONFIG_SPICE.  Due to QAPI
limitations, we need a dummy function anyway, but it's unreachable.

Our current dummy function goes out of its way to produce the exact
same error as the QMP core does for unknown commands.  Cute, but both
unclean and unnecessary.  Replace by straight abort().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>

qmp.c

@@ -137,14 +137,18 @@ VncInfo *qmp_query_vnc(Error **errp)
 #endif
 
 #ifndef CONFIG_SPICE
-/* If SPICE support is enabled, the "true" query-spice command is
-   defined in the SPICE subsystem. Also note that we use a small
-   trick to maintain query-spice's original behavior, which is not
-   to be available in the namespace if SPICE is not compiled in */
+/*
+ * qmp-commands.hx ensures that QMP command query-spice exists only
+ * #ifdef CONFIG_SPICE.  Necessary for an accurate query-commands
+ * result.  However, the QAPI schema is blissfully unaware of that,
+ * and the QAPI code generator happily generates a dead
+ * qmp_marshal_input_query_spice() that calls qmp_query_spice().
+ * Provide it one, or else linking fails.
+ * FIXME Educate the QAPI schema on CONFIG_SPICE.
+ */
 SpiceInfo *qmp_query_spice(Error **errp)
 {
-    error_set(errp, QERR_COMMAND_NOT_FOUND, "query-spice");
-    return NULL;
+    abort();
 };
 #endif