qerror.h: Remove QERR defines that are only used once

Just hardcode them in the callers

Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c
index 921de33..9c61449 100644
--- a/qapi/qmp-dispatch.c
+++ b/qapi/qmp-dispatch.c
@@ -80,7 +80,8 @@
         return NULL;
     }
     if (!cmd->enabled) {
-        error_set(errp, QERR_COMMAND_DISABLED, command);
+        error_setg(errp, "The command %s has been disabled for this instance",
+                   command);
         return NULL;
     }