MDL-87425 core: Remove the deprecated code

.upgradenotes/MDL-87425-2025123010293153.yml

@@ -0,0 +1,7 @@
+issueNumber: MDL-87425
+notes:
+  core:
+    - message: >-
+        The `MOD_PURPOSE_INTERFACE` constant has been removed from
+        `public/lib/moodlelib.php`.
+      type: removed

public/admin/tool/componentlibrary/content/moodle/components/activityicons.md

@@ -127,8 +127,6 @@ Since Moodle 4.4, the available activity purposes are:
 * Resource (MOD_PURPOSE_CONTENT)
 * Other (MOD_PURPOSE_OTHER)
 
-> NOTE: On Moodle 4.3 downwards, MOD_PURPOSE_INTERFACE was also available, but it has been deprecated, so it's not recommended to use it.
-
 ### Purpose colours
 
 The activity icon colours can be customised using the theme Boost 'Raw initial SCSS' feature. The following variables are available:

public/lib/moodlelib.php

@@ -500,12 +500,6 @@ define('MOD_PURPOSE_CONTENT', 'content');
 define('MOD_PURPOSE_INTERACTIVECONTENT', 'interactivecontent');
 /** Module purpose other */
 define('MOD_PURPOSE_OTHER', 'other');
-/**
- * Module purpose interface
- * @deprecated since Moodle 4.4
- * @todo MDL-80701 Remove in Moodle 4.8
-*/
-define('MOD_PURPOSE_INTERFACE', 'interface');
 
 /** True if module can be quickly created without filling a previous form. */
 define('FEATURE_QUICKCREATE', 'quickcreate');