Comment form appering only with a title field if content type of that node is deleted

Follower of #400450: Be more graceful when editing nodes with disabled node types and #232327: Deleting node type leaves orphan nodes .

Steps to reproduce:

1. Add couple of nodes for a particular content type with comments enabled for a content type
2. Go ahead and delete that content type
3. Goto node/% page of content you just created
4. Here you will see a comment add form only with title (NO body) and you can still add comments.

Suggested solution:

Remove comment form from node view if content type of particular content type is been deleted/disabled.