Remove renderMode: 'image' for vector tile layers

src/ol/layer/VectorTile.js

@@ -36,10 +36,6 @@ import {assign} from '../obj.js';
  * the largest possible buffer of the used tiles. It should be at least the size of the largest
  * point symbol or line width.
  * @property {import("./VectorTileRenderType.js").default|string} [renderMode='hybrid'] Render mode for vector tiles:
- *  * `'image'`: Vector tiles are rendered as images. Only available when `declutter` is set to `false` (default).
- *    Otherwise, `'hybrid'` mode will used instead. Great performance, but point symbols and texts
- *    are always rotated with the view and pixels are scaled during zoom animations. Labels and point symbols will
- *    get cut off at tile boundaries.
  *  * `'hybrid'`: Polygon and line elements are rendered as images, so pixels are scaled during zoom
  *    animations. Point symbols and texts are accurately rendered as vectors and can stay upright on
  *    rotated views.
@@ -93,14 +89,19 @@ class VectorTileLayer extends BaseVectorLayer {
 
     super(/** @type {import("./BaseVector.js").Options} */ (baseOptions));
 
-    const renderMode = options.renderMode || VectorTileRenderType.HYBRID;
+    let renderMode = options.renderMode || VectorTileRenderType.HYBRID;
+    if (renderMode === VectorTileRenderType.IMAGE) {
+      //FIXME deprecated - remove this check in v7.
+      //eslint-disable-next-line
+      console.warn('renderMode: "image" is deprecated. Option ignored.')
+      renderMode = undefined;
+    }
     assert(
       renderMode == undefined ||
-        renderMode == VectorTileRenderType.IMAGE ||
         renderMode == VectorTileRenderType.HYBRID ||
         renderMode == VectorTileRenderType.VECTOR,
       28
-    ); // `renderMode` must be `'image'`, `'hybrid'` or `'vector'`.
+    ); // `renderMode` must be `'hybrid'` or `'vector'`.
 
     /**
      * @private