Magento – Magento2: How to remove ‘My Orders’ in Luma sidebar

I recommend that you take the form.phtml, copy it, then customize it inside your module.

Put customForm.phtml in design/adminhtml/default/default/template/modulename/. Next, you will need to enter the new customForm.phtml into your xml layout file. Copy over the Mage/core/adminhtml/etc/config.xml entry for

<adminhtml_sales_order_shipment_new>  

Copy that whole node. You're going to need all the block entries to do a succesful override. Then, change the specific form call to your custom form. The ... in the code below denotes all the other xml you will have copied over.

<layout>
    <adminhtml_sales_order_shipment_new>
        ...
        <reference name="content">
            ...
            <block type="adminhtml/sales_order_shipment_create_form" template="modulename/customForm.phtml">    
            </block>
            ...
        </reference>
    </adminhtml_sales_order_shipment_new>
</layout>

This way, you can customize the form to your hearts content, and the post action will include your variables.

Notice that I did not change the type. You do not need to change this specific block to do what you're doing. If you look at Mage_Adminhtml_Sales_Order_Shipment_Create_Form, you'll see all it does is execute layout calls, assign urls, child html, etc. You can probably leave it alone.

Via layout XML (although this will remove the whole block including the container):

<remove name="left" />

Programmatically: In your config.xml, listen to the event core_block_abstract_to_html_before (this will keep the container, but will remove all child blocks):

<core_block_abstract_to_html_before>
    <observers>
        <your_extension>
            <class>your_extension/observer</class>
            <method>coreBlockAbstractToHtmlBefore</method>
        </your_extension>
    </observers>
<core_block_abstract_to_html_before>

And then in your Observer.php, unset all children if the current block is the block of the left sidebar:

public function coreBlockAbstractToHtmlBefore(Varien_Event_Observer $observer) {
    /* @var Mage_Core_Block_Abstract $block */
    $block = $observer->getEvent()->getBlock();
    if ($block->getNameInLayout() == 'left') {
        $block->unsetChildren();
    }
}