Remove unused WebGLShader class

src/ol/webgl/Shader.js

@@ -1,48 +0,0 @@
-/**
- * @module ol/webgl/Shader
- */
-import {abstract} from '../util.js';
-
-/**
- * @abstract
- */
-class WebGLShader {
-
-  /**
-   * @param {string} source Source.
-   */
-  constructor(source) {
-
-    /**
-     * @private
-     * @type {string}
-     */
-    this.source_ = source;
-
-  }
-
-  /**
-   * @return {boolean} Is animated?
-   */
-  isAnimated() {
-    return false;
-  }
-
-  /**
-   * @abstract
-   * @return {number} Type.
-   */
-  getType() {
-    return abstract();
-  }
-
-  /**
-   * @return {string} Source.
-   */
-  getSource() {
-    return this.source_;
-  }
-}
-
-
-export default WebGLShader;