Only use the global fish_complete_path and fish_function_path

Prior to this fix, fish would attempt to react if a local fish_complete_path
or fish_function_path were set. However this has never been very well tested
and will become impossible with concurrent execution. Always use the global
values.

src/function.cpp

@@ -104,7 +104,7 @@ static void try_autoload(const wcstring &name, parser_t &parser) {
     {
         auto funcset = function_set.acquire();
         if (funcset->allow_autoload(name)) {
-            path_to_autoload = funcset->autoloader.resolve_command(name, parser.vars());
+            path_to_autoload = funcset->autoloader.resolve_command(name, env_stack_t::globals());
         }
     }