Remove redundant comments with hash rocket

The comment comments out a line of old code. This should generally not
be left in the codebase as the code can be retrieved using source
control.
Replace forgotten symbol key hash rockets

The symbol key hash rockets in the controller and routes.rb are somehow
missed by the `hash_rocket` gem. They got replaced, however, when
rerunning `hash_rocket`.

The Rake task files have a different suffix, which are missed when
running `hash_rocket`.
Replace symbol key hash rockets in comments

These code snippets are meaningful to be left in comments.
Replace symbol hash rocket in embbeded ERB string
Merge pull request #1521 from zhangsu/remaining_hash_rockets

Replace or remove remaining hash rockets