[feature/remove-db-styles] Removed database storage of style components.

The bulk of database storage of templates is removed, rendering template
stored in the database as useless.

Theme database storage is reduced to a skeleton for full removal soon.

This commit was cherry picked from the old feature/ascraeus-experiment branch
the old commit hash is 0dbe7e3b6c.

PHPBB3-9741

phpBB/install/index.php

@@ -205,9 +205,6 @@ $template->set_custom_template('../adm/style', 'admin');
 $template->assign_var('T_ASSETS_PATH', '../assets');
 $template->assign_var('T_TEMPLATE_PATH', '../adm/style');
 
-// the acp template is never stored in the database
-$user->theme['template_storedb'] = false;
-
 $install = new module();
 
 $install->create('install', "index.$phpEx", $mode, $sub);