Wordpress remove category URL without Plugin

function fix_slash( $string, $type )
{
global $wp_rewrite;
if ( $wp_rewrite->use_trailing_slashes == false )
{
    if ( $type != 'single' && $type != 'category' )
        return trailingslashit( $string );

    if ( $type == 'single' && ( strpos( $string, '.html/' ) !== false ) )
        return trailingslashit( $string );

    if ( $type == 'category' && ( strpos( $string, 'category' ) !== false ) )
    {
        $aa_g = str_replace( "/category/", "/", $string );
        return trailingslashit( $aa_g );
    }
    if ( $type == 'category' )
        return trailingslashit( $string );
}
return $string;
}

add_filter( 'user_trailingslashit', 'fix_slash', 55, 2 );