gistfile1.php

<?php

class SomeModelAdmin extends ModelAdmin {

	private static $managed_models = array(
		"MyDataObject"
	);

	public function getEditForm($id = null, $fields = null) {
		$form = parent::getEditForm($id, $fields);

		$gridField = $form->Fields()->dataFieldByName('MyDataObject');
		$detailForm = $gridField->getConfig()->getComponentByType('GridFieldDetailForm');
		
		$detailForm->setItemEditFormCallback(function($form) use ($self) {
			$form->Actions()->removeByName('action_doDelete');
		});

		return $form;
	}

}