Don't define functions in the prototype

If `VOID` is used, TypeScript is not able to figure out what the function parameters are.

Before:
```
$ npx tsc | wc -l
    1188
```

After:
```
$ npx tsc | wc -l
    1169
```

src/ol/webgl/Shader.js

@@ -1,7 +1,6 @@
 /**
  * @module ol/webgl/Shader
  */
-import {FALSE} from '../functions.js';
 
 /**
  * @abstract
@@ -21,6 +20,13 @@ class WebGLShader {
 
   }
 
+  /**
+   * @return {boolean} Is animated?
+   */
+  isAnimated() {
+    return false;
+  }
+
   /**
    * @abstract
    * @return {number} Type.
@@ -36,8 +42,4 @@ class WebGLShader {
 }
 
 
-/**
- * @return {boolean} Is animated?
- */
-WebGLShader.prototype.isAnimated = FALSE;
 export default WebGLShader;