How do you delete a CCK field?

I have the exact same problem.

http://drupal.org/project/content_type_cleanup

I searched the CCK issues but couldn't find anything there. You can delete it from the database but you must be very careful to do so.
Before going into the database I think you should do these:

• delete any cck nodes that use that field
• remove the field from any content type which included it
• make sure you are not using a view that references that field. if so remove the field from that view also.
• if you are using any contributed module that may use that field, you should go and remove the field from that module's components.
• now we can move to the database. check each content_type_* table and remove the field row if it is still there.
• check node_field table and delete the field row there.
• check node_field_instance table and delete the field rows there.
• check node_group_fields table and delete the field row from there. this is added by the field group module I think. so you may not have it.
• finally find the table content_field_* where * is your field's name and then remove that table altogether.

As you can see this is very error prune and you may miss something. Actually I am not sure if I miss anything above. So the more correct action to take is open a CCK issue at the project page.

Under "Administer" > "Content management" > "Content types" cliick edit for the content type you want to remove the field from. Then click the "Manage fields" tab. If the field can be removed it there will be a 'remove' link under 'Operations'.

It appears if you remove a field from all content types, the system removes it. That is probably why the field list doesn't have an actual delete button. Not intuitive, but it works.

$type = 'mytype';
$content = content_types($type);
if (count($content['fields']) > 0){
include_once('./'. drupal_get_path('module', 'content') .'/content_crud.inc');
foreach($content['fields'] as $key => $field){
content_field_instance_delete(array('type_name'=>$class->pcid,'field_name'=>$key));
}
}

Just change the number of values (I don't know whether this is the right english translation) to number of fields you want. Now you've got the right number of fields, if you want to add another field just set the number of values back to unlimited.

Tread lightly when doing this, and backup your database beforehand. Make sure none of the inactive fields are used on other content types.

     $content_type = 'franchise';
    $inactive_fields = content_inactive_fields($content_type);

    foreach($inactive_fields as $field_name => $field) {
      
    $used_on_other_content_type = (int) db_result(db_query("select 1 from content_node_field_instance WHERE field_name like '%s' and type_name != '%s' LIMIT 1",$field_name, $content_type));
    
      if(!$used_on_other_content_type) {
        if($field['multiple'] == 0) {
            foreach($field['columns'] as $column_key => $column) {
              db_query("ALTER TABLE content_type_%s DROP column %s",$content_type, $field_name.'_'.$column_key);
            }
          } 
        else {
          // if multiple, uses a separate table
          db_query("DROP TABLE %s",'content_'.$field_name);
          db_query("DROP TABLE %s",'node_data_'.$field_name);
        }
          
        db_query("DELETE FROM content_node_field WHERE field_name = '%s'",$field_name);
        db_query("DELETE FROM content_node_field_instance WHERE field_name = '%s' AND type_name = '%s'",$field_name, $content_type);
     }
    } 

In drupal 6 there is a function content_field_instance_delete that deletes fields. If there are no remaining instances it will delete the column or table.