monitor: Drop do_qmp_capabilities()'s superfluous QMP check

Superfluous since commit 30f5041e removed it from HMP.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NLuiz Capitulino <lcapitulino@redhat.com>

monitor.c

@@ -566,11 +566,7 @@ static void monitor_qapi_event_init(void)
 static int do_qmp_capabilities(Monitor *mon, const QDict *params,
                                QObject **ret_data)
 {
-    /* Will setup QMP capabilities in the future */
-    if (monitor_ctrl_mode(mon)) {
-        mon->qmp.command_mode = 1;
-    }
-
+    mon->qmp.command_mode = 1;
     return 0;
 }