In the async version of the client creation, i.e. when a new client
is created via bolt_client_new_async and an error happens it will be
passed to g_task_return_error which takes ownership of it but the very
same error will also be free'd via g_autoptr; remove the latter.

This is a port of bolt commit e96f8bd47587b167ae46c8ac9347003f69f931dd