Fixed a bunch of PHP 7.4 syntax errors

- FIX: Removed pointless (and invalid) destructor in LinkedIn::__destruct()
- FIX: All files that trigger this deprecation notice in PHP 7.4:
       "Array and string offset access syntax with curly braces is deprecated"

e107_plugins/forum/e_list.php

@@ -115,7 +115,7 @@ class list_forum
 					}
 					else
 					{
-						if($thread_lastuser{0} == "0")
+						if($thread_lastuser[0] == "0")
 						{
 							$LASTPOST = substr($thread_lastuser, 2);
 						}