Issue #2330943 by herom: Remove mention of hook_date_format_types() in docs.

core/includes/common.inc

@@ -593,8 +593,7 @@ function format_size($size, $langcode = NULL) {
  *   - One of the built-in formats: 'short', 'medium',
  *     'long', 'html_datetime', 'html_date', 'html_time',
  *     'html_yearless_date', 'html_week', 'html_month', 'html_year'.
- *   - The name of a date type defined by a module in
- *     hook_date_format_types(), if it's been assigned a format.
+ *   - The name of a date type defined by a date format config entity.
  *   - The machine name of an administrator-defined date format.
  *   - 'custom', to use $format.
  *   Defaults to 'medium'.

core/lib/Drupal/Core/Datetime/DateFormatter.php

@@ -103,8 +103,7 @@ public function __construct(EntityManagerInterface $entity_manager, LanguageMana
    *   - One of the built-in formats: 'short', 'medium',
    *     'long', 'html_datetime', 'html_date', 'html_time',
    *     'html_yearless_date', 'html_week', 'html_month', 'html_year'.
-   *   - The name of a date type defined by a module in
-   *     hook_date_format_types(), if it's been assigned a format.
+   *   - The name of a date type defined by a date format config entity.
    *   - The machine name of an administrator-defined date format.
    *   - 'custom', to use $format.
    *   Defaults to 'medium'.