(SystemHealth) remove unused model

src/opnsense/mvc/app/models/OPNsense/SystemHealth/SystemHealth.php

-<?php
-/**
- *    Copyright (C) 2015 Deciso B.V.
- *
- *    All rights reserved.
- *
- *    Redistribution and use in source and binary forms, with or without
- *    modification, are permitted provided that the following conditions are met:
- *
- *    1. Redistributions of source code must retain the above copyright notice,
- *       this list of conditions and the following disclaimer.
- *
- *    2. Redistributions in binary form must reproduce the above copyright
- *       notice, this list of conditions and the following disclaimer in the
- *       documentation and/or other materials provided with the distribution.
- *
- *    THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
- *    INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
- *    AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
- *    AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
- *    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
- *    SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
- *    INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
- *    CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- *    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
- *    POSSIBILITY OF SUCH DAMAGE.
- *
- */
-namespace OPNsense\SystemHealth;
-
-use OPNsense\Base\BaseModel;
-
-class Sample extends BaseModel
-{
-}

src/opnsense/mvc/app/models/OPNsense/SystemHealth/SystemHealth.xml

-<model>
-    <mount>//OPNsense/systemhealth</mount>
-    <description>
-        (rrd) System Health Settings
-    </description>
-    <items>
-    </items>
-</model>