Remove legacy auth usage of $_SESSION (#10491)

* Remove auth use of $_SESSION

Will break plugins that depend on $_SESSION, Weathermap was already fixed.
Port them to use Auth::check()/Auth::user()/Auth:id()

* revert accidental replacement

includes/html/pages/plugin/admin.inc.php

@@ -1,8 +1,6 @@
 <?php
 
-use LibreNMS\Authentication\LegacyAuth;
-
-if (LegacyAuth::user()->hasGlobalAdmin()) {
+if (Auth::user()->hasGlobalAdmin()) {
     // Scan for new plugins and add to the database
     $new_plugins = scan_new_plugins();