STYLES parameter duplicated on getFeatureInfo 

Hi,

With the code sample below an extra STYLES paramater is added to the getFeatureInfo request instead of replacing the default paramater 

The following request is submitted

/geoserver/VO/wms?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetFeatureInfo&FORMAT=image%2Fpng&TRANSPARENT=true&WIDTH=256&HEIGHT=256&LAYERS=HO%3APost%20Visit&QUERY_LAYERS=HO%3APost%2Visit&**STYLES**=&CRS=EPSG%3A2157&BBOX=559483.5961953121%2C572078.5322421874%2C562977.9180781246%2C575572.854125&INFO_FORMAT=application%2Fjson&I=213&J=187&FEATURE_COUNT=999&**STYLES**=point
```javascript
var layers = [
  new ol.layer.Tile({
    source: new ol.source.TileWMS({
      url: gsURL,
      crossOrigin: 'anonymous',
      attributions: [new ol.Attribution({
        html: '&copy; HO ' 
      })],
      params: {
        'LAYERS': 'HO:Post Visit',
        'FORMAT': 'image/png'
      },
      extent: ITM_EXTENT,
      getFeatureInfoOptions: {
          method: 'xhr_get',
          params: {
            'INFO_FORMAT': 'application/json',
            'FEATURE_COUNT': '999',
            'STYLES' : 'point'
          }
        }
    })
  })
];
```