Can’t remove woocommerce sidebar

First, most themes have multiple page templates you can choose from.

Please check:

1. go to cart page (in wp-admin).
2. See side metabox ‘Page Attributes’.
3. There you can set the page template, does it have something like ‘full_width’?

You can also try a different hook, like wp_head.

Example:

add_action( 'wp_head', 'urun_sidebar_kaldir' );

Let me know.

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After checking the WOO cart template, i can’t find a do_action( 'woocommerce_sidebar' ).
It does exist in the singe-product.php template.

Are you certain the cart sidebar is generated by WooCommerce?

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Add a full-width template to your theme:

Read this.

Then follow the steps i mentiod at the beginning of my answer.