Removing rules from .htaccess

Problem 1

Your hook ci_add_rules() will still run when you flush rules, so remove it first (and avoid “unsetting” non_wp_rules, you’ll break other plugins that make use of it).

function ci_remove_rules()
{
    remove_action( 'generate_rewrite_rules', 'ci_add_rules' );
    $GLOBALS['wp_rewrite']->flush_rules();
}

Problem 2

Pretty sure you want:

plugin_dir_url( 'proxy.php', __FILE__ )

..instead of:

plugin_dir_path( __FILE__ ) . 'proxy.php