// 1. Remove the description product tab
add_filter( 'woocommerce_product_tabs', 'remove_descrip_product_tab', 98 );
function remove_descrip_product_tab( $tabs ) {
    // Remove the description tab
    unset( $tabs['description'] );

    return $tabs;
}

// 2. Add the product description after the product short description
add_action( 'woocommerce_single_product_summary', 'my_custom_action', 25 );
function my_custom_action() {
    global $post;;

    // Product description output
    echo '<div class="product-post-content">' . the_content() . '</div>';
}