If you need to remove a template_redirect from within a custom plugin, simply using remove_action( 'template_redirect', 'function_to_remove' ); won’t cut it.

As a workaround, what you can do is create a function to hook into template_redirect action earlier and then remove the redirect you are trying to remove.

// remove a template redirect from within a custom plugin.
add_action( 'template_redirect', 'remove_my_action', 5 );
function remove_my_action(){
    remove_action('template_redirect', 'function_to_remove', 10 );
}