rm [frontend backbone] template caching

  - The only templates we fetch like this are wigdet edit templates
  - The templates are cleared on save
  - This means the only time we had a cache hit was when you do 'edit',
    'cancel', 'edit'. This almost never happens, and when it does, it's
    during development when you want a new template.

If there's a different use case in the future, this might be worthwhile
to put back, but it's useless code right now.