Remove setDeclutter function

Changing the declutter value after the layer creating doesn't work, remove the function to avoid confusion.

src/ol/layer/BaseVector.js

@@ -133,13 +133,6 @@ class BaseVectorLayer extends Layer {
     return this.declutter_;
   }
 
-  /**
-   * @param {boolean} declutter Declutter.
-   */
-  setDeclutter(declutter) {
-    this.declutter_ = declutter;
-  }
-
   /**
    * @return {number|undefined} Render buffer.
    */