Deleting Files from an Organization

The package.xml file is a project manifest that lists all the components to retrieve or deploy. Although you can use package.xml to add components, it’s not sufficient to delete them. 
To delete files, create a delete manifest that’s called destructiveChanges.xml. The format of the delete manifest is the same as package.xml, except that wildcards aren’t supported

The following sample destructiveChanges.xml file names a single custom object to be deleted:

1	<?xml version="1.0" encoding="UTF-8"?>

2	<Package xmlns="http://soap.sforce.com/2006/04/metadata">

3

<types>

4	<members>MyCustomObject__c</members>

5	<name>CustomObject</name>

6

</types>

7	</Package>

To deploy the destructive changes, you must also have a package.xml file that lists no components to deploy, includes the API version, and is in the same directory as destructiveChanges.xml:

1	<?xml version="1.0" encoding="UTF-8"?>

2	<Package xmlns="http://soap.sforce.com/2006/04/metadata">

3	<version>38.0</version>

4	</Package>

• To bypass the Recycle Bin, set the purgeOnDelete option to true.
• If you try to delete some components that don’t exist in the organization, the rest of the deletions are still attempted.

Delete Apex Code From Production using workbench

1.Download the zip file and add  all classes in destructiveChange.xml
2.Make again the zip file combing both the files

and deploy as screenshot shows