Remove all @deprecated code from menu_link_content module

@hardik, Comment there in code itself explain that we had converted from array to string as "The possibility to pass an array as source value to the plugin will be removed in drupal:9.0.0. Pass a string value instead." So we don't have to remove entire code. As test case failed due to removing of reset() from your patch as $value is array.

Please review updated patch.

@dhirendra.mishra @Hardik_Patel_12, #6 patch works fine. Thanks for your valuable contribution.

+++ b/core/modules/menu_link_content/src/Plugin/migrate/process/LinkUri.php
@@ -90,9 +90,7 @@ public static function create(ContainerInterface $container, array $configuratio
     if (is_array($value)) {
       $value = reset($value);
-      @trigger_error('Passing an array as source value into the link_uri migrate process plugin is deprecated in drupal:8.8.0. The possibility to pass an array as source value to the plugin will be removed in drupal:9.0.0. Pass a string value instead. See https://www.drupal.org/node/3043694', E_USER_DEPRECATED);
     }

We need to remove the entire if here. That behaviour is deprecated. And remove the corresponding test - i.e. \Drupal\Tests\menu_link_content\Kernel\Plugin\migrate\process\LinkUriTest::testRoutedLegacy()

Fixed as per mentioned in #10 and interdiff from #2 patch.

Thanks @dhirendra.mishra , I see the suggestions by @alexpott have been successfully applied in patch.

Committed 839caad and pushed to 9.0.x. Thanks!