Simplify the uninstall clean up

imageapi_optimize.install

@@ -6,9 +6,5 @@
  */
 
 function imageapi_optimize_uninstall() {
-  variable_del('imageapi_optimize_toolkit');
-  variable_del('imageapi_optimize_advpng');
-  variable_del('imageapi_optimize_optipng');
-  variable_del('imageapi_optimize_jpegtran');
-  variable_del('imageapi_optimize_jiffremove');
+  db_query("DELETE FROM {variable} WHERE name LIKE 'imageapi_optimize_%'");
 }