[REF] web: remove select2 from backend assets

The select2 library is only used in the frontend, now that the last
backend usecase (AceEditor) has been removed. This commit thus
removes the select2 library from the backend assets.

Part-of: odoo/odoo#139154

addons/web/__manifest__.py

@@ -54,8 +54,6 @@ This module provides the core of the Odoo Web Client.
             'web/static/lib/jquery.ui/jquery-ui.css',
             'web/static/src/libs/fontawesome/css/font-awesome.css',
             'web/static/lib/odoo_ui_icons/*',
-            'web/static/lib/select2/select2.css',
-            'web/static/lib/select2-bootstrap-css/select2-bootstrap.css',
             'web/static/src/webclient/navbar/navbar.scss',
             'web/static/src/scss/animation.scss',
             'web/static/src/scss/fontawesome_overridden.scss',
@@ -87,7 +85,6 @@ This module provides the core of the Odoo Web Client.
             'web/static/lib/bootstrap/js/dist/scrollspy.js',
             'web/static/lib/bootstrap/js/dist/tab.js',
             'web/static/lib/bootstrap/js/dist/toast.js',
-            'web/static/lib/select2/select2.js',
             'web/static/lib/clipboard/clipboard.js',
             'web/static/src/legacy/js/libs/autocomplete.js',
             'web/static/src/legacy/js/libs/bootstrap.js',