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/geom/Geometry.js

@@ -3,7 +3,6 @@
  */
 import BaseObject from '../Object.js';
 import {createEmpty, getHeight, returnOrUpdate} from '../extent.js';
-import {FALSE} from '../functions.js';
 import {transform2D} from '../geom/flat/transform.js';
 import {get as getProjection, getTransform} from '../proj.js';
 import Units from '../proj/Units.js';
@@ -82,6 +81,15 @@ class Geometry extends BaseObject {
    */
   closestPointXY(x, y, closestPoint, minSquaredDistance) {}
 
+  /**
+   * @param {number} x X.
+   * @param {number} y Y.
+   * @return {boolean} Contains (x, y).
+   */
+  containsXY(x, y) {
+    return false;
+  }
+
   /**
    * Return the closest point of the geometry to the passed point as
    * {@link module:ol/coordinate~Coordinate coordinate}.
@@ -248,12 +256,4 @@ class Geometry extends BaseObject {
 }
 
 
-/**
- * @param {number} x X.
- * @param {number} y Y.
- * @return {boolean} Contains (x, y).
- */
-Geometry.prototype.containsXY = FALSE;
-
-
 export default Geometry;