removed deprecated code from render system

Closes #3441392

core/lib/Drupal/Component/Render/FormattableMarkup.php

@@ -130,9 +130,8 @@ public function jsonSerialize(): string {
    *   An associative array of replacements. Each array key should be the same
    *   as a placeholder in $string. The corresponding value should be a string
    *   or an object that implements \Drupal\Component\Render\MarkupInterface.
-   *   Null args[] values are deprecated in Drupal 9.5 and will fail in
-   *   Drupal 11.0. The value replaces the placeholder in $string. Sanitization
-   *   and formatting will be done before replacement. The type of sanitization
+   *   The args[] value replaces the placeholder in $string. Sanitization and
+   *   formatting will be done before replacement. The type of sanitization
    *   and formatting depends on the first character of the key:
    *   - @variable: When the placeholder replacement value is:
    *     - A string, the replaced value in the returned string will be sanitized
@@ -194,15 +193,6 @@ public function jsonSerialize(): string {
   protected static function placeholderFormat($string, array $args) {
     // Transform arguments before inserting them.
     foreach ($args as $key => $value) {
-      if (is_null($value)) {
-        // It's probably a bug to provide a null value for the placeholder arg,
-        // and in D11 this will no longer be allowed. When this trigger_error
-        // is removed, also remove isset $value checks inside the switch{}
-        // below.
-        // phpcs:ignore Drupal.Semantics.FunctionTriggerError
-        @trigger_error(sprintf('Deprecated NULL placeholder value for key (%s) in: "%s". This will throw a PHP error in drupal:11.0.0. See https://www.drupal.org/node/3318826', (string) $key, (string) $string), E_USER_DEPRECATED);
-        $value = '';
-      }
       switch ($key[0]) {
         case '@':
           // Escape if the value is not an object from a class that implements