Tests: Remove redundant wp_image_editors filter.

The `WP_Tests_Image_Resize_UnitTestCase` class extends `WP_Image_UnitTestCase`, which already has a `wp_image_editors` filter performing the same action.

This also officially declares `$editor_engine` as a property in the base class.

Props mukesh27.
See #63167.

git-svn-id: https://develop.svn.wordpress.org/trunk@60763 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

tests/phpunit/tests/image/base.php

@@ -5,6 +5,13 @@
  */
 abstract class WP_Image_UnitTestCase extends WP_UnitTestCase {
 
+	/**
+	 * The image editing library class to use in tests.
+	 *
+	 * @var string
+	 */
+	public $editor_engine;
+
 	/**
 	 * Set the image editor engine according to the unit test's specification
 	 */

tests/phpunit/tests/image/resize.php

@@ -12,12 +12,6 @@ abstract class WP_Tests_Image_Resize_UnitTestCase extends WP_Image_UnitTestCase
 
 	public function set_up() {
 		parent::set_up();
-
-		add_filter( 'wp_image_editors', array( $this, 'wp_image_editors' ) );
-	}
-
-	public function wp_image_editors() {
-		return array( $this->editor_engine );
 	}
 
 	public function test_resize_jpg() {