Webgl points / use default vertex shader for hit detection

Otherwise we were getting errors if the custom
vertex shader was missing varyings expected by
HIT_FRAGMENT_SHADER.

src/ol/renderer/webgl/PointsLayer.js

@@ -245,7 +245,7 @@ class WebGLPointsLayerRenderer extends WebGLLayerRenderer {
     );
     this.hitProgram_ = this.helper.getProgram(
       HIT_FRAGMENT_SHADER,
-      options.vertexShader || VERTEX_SHADER
+      VERTEX_SHADER
     );
 
     this.sizeCallback_ = options.sizeCallback || function() {