Override woocommerce wc-class function

I'm not good in WP and plugins and will need some help here. I've read that is possible to alter some WC core function with filters and action but probably I didn't understand this correctly. I want to simply delete the shipping price from my cart page Total price field.

The function which is in woocommerce/includes/class-wc-cart-totals.php is:

protected function calculate_totals() {
    $this->set_total( 'total', round( $this->get_total( 'items_total', true ) + $this->get_total( 'fees_total', true ) + $this->get_total( 'shipping_total', true ) + array_sum( $this->get_merged_taxes( true ) ), 0 ) );
    $this->cart->set_total_tax( array_sum( $this->get_merged_taxes( false ) ) );

    // Allow plugins to hook and alter totals before final total is calculated.
    if ( has_action( 'woocommerce_calculate_totals' ) ) {
        do_action( 'woocommerce_calculate_totals', $this->cart );
    }

    // Allow plugins to filter the grand total, and sum the cart totals in case of modifications.
    $this->cart->set_total( max( 0, apply_filters( 'woocommerce_calculated_total', $this->get_total( 'total' ), $this->cart ) ) );
}

I've tried to copy it to my child theme function.php file like this:

add_action('calculate_totals', 'my_calculate_totals');

function my_calculate_totals() 
{
        $this->set_total( 'total', round( $this->get_total( 'items_total', true ) + $this->get_total( 'fees_total', true ) + array_sum( $this->get_merged_taxes( true ) ), 0 ) );
        $this->cart->set_total_tax( array_sum( $this->get_merged_taxes( false ) ) );

        // Allow plugins to hook and alter totals before final total is calculated.
        if ( has_action( 'woocommerce_calculate_totals' ) ) {
            do_action( 'woocommerce_calculate_totals', $this->cart );
        }

        // Allow plugins to filter the grand total, and sum the cart totals in case of modifications.
        $this->cart->set_total( max( 0, apply_filters( 'woocommerce_calculated_total', $this->get_total( 'total' ), $this->cart ) ) );
}

It doesn't work. Is this possible?

My goal is to just remove this from first line

$this->get_total( 'shipping_total', true )

UPDATE:

I have tried like this

add_action( 'woocommerce_calculate_totals', 'my_calculate_totals');

function my_calculate_totals($cart = null) 
{
        $cart = new WC_Cart_Totals();
        $this->set_total( 'total', round( $this->get_total( 'items_total', true ) + $this->get_total( 'fees_total', true ) + array_sum( $this->get_merged_taxes( true ) ), 0 ) );
        $this->cart->set_total_tax( array_sum( $this->get_merged_taxes( false ) ) );

}

Got this error

A valid WC_Cart object is required