OpenLayers WFS Layer with OpenLayers.Request.Get

HTML

<link rel="stylesheet" href="https://openlayers.org/en/v4.6.5/css/ol.css">
<script src="https://openlayers.org/en/v4.6.5/build/ol-debug.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/proj4js/2.2.1/proj4.js"></script>
<script src="http://epsg.io/23030.js"></script>
<body  >
 
    <div id="map"></div>
</body>

CSS

#map {
    width: 100%;
    height: 500px;
}

JavaScript

var gml = `<FeatureCollection xmlns:gml="http://www.opengis.net/gml" xmlns:fme="http://www.safe.com/gml/fme" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"          Subcuencas_semidetalle.xsd">
     <boundedBy>
        <Envelope srsName="EPSG:23030" srsDimension="2">
           <lowerCorner>100526.0003 3987304.0001</gml:lowerCorner>
           <upperCorner>621651.8125 4288889.0001</gml:upperCorner>
        </Envelope>
     </boundedBy>
     <featureMember>
        
           <surfaceProperty>
              <Surface srsName="EPSG:23030" srsDimension="2">
                 <patches>
                    <PolygonPatch>
                       <exterior>
                          <LinearRing>
                             <posList>517055.4077 4226197.9999 517169.4065 4226127.0009 517264.0937 4226050.9997 517329.8121 4226008.9993 517516.3142 4225897.9997 517634.9067 4225840.9999 517694.3121 4225781.9999 517794.9057 4225712.9999 517925.3131 4225600.0003 518031.4999 4225461.0005 518001.9995 4225351.0005 517635.5938 4225332.0001 517525.5937 4225301.9999 517375.4067 4225227.9985 517271.6877 4225165.0001 517168.0937 4225050.0007 517129.9999 4224967.9999 517071.0933 4224811.9997 516925.3127 4224590.0005 516823.8127 4224498.9997 516696.9063 4224397.0001 516576.1879 4224261.0005 516532.0003 4224167.9999 516489.8125 4224100.0001 516465.8121 4224027.9997 516388.0935 4223856.9999 516229.906 4223735.9999 516139.3127 4223671.9999 516045.4999 4223831.0005 516025.3129 4223913.9997 515994.4997 4224011.9997 515972.9997 4224181.0005 515869.0945 4224299.9997 515824.5003 4224361.9997 515654.9997 4224402.0003 515585.4997 4224459.0001 515525.5937 4224571.9997 515459.9061 4224633.0003 515324.3121 4224704.0003 515285.5937 4225095.9999 515233.6871 4225206.9995 515180.3121 4225269.9999 515040.8127 4225388.0007 515007.4999 4225565.0001 514969.3129 4225634.9997 514757.4063 4225705.0003 514690.5933 4225772.9991 514632.1865 4225870.9999 514591.6873...