To remove predefined templates (Blog, Form Template) remove this paths in crxde:
/libs/collab/commons/templates/form
/libs/collab/blog/templates/page
To remove your templates:
1) Create page with template to remove (to check template path)
2) Check template path in crxde: /content/your_app/your_page/jcr:content in property cq:template
3) Remove template path (and temporary page)