Replace or remove remaining hash rockets

This is for #1498 and includes

1. Removing or replacing symbol key hash rockets in comments
2. Replacing symbol key hash rockets in ERB embedded in a string literal.
3. Replacing symbol key hash rockets in files that were not captured by the
`hash_syntax` gem (route.rb, *.rake, etc.)

the style issues in the changed lines are not being dealt with so that errors
are minimized and code review is easier.

As a result, please ignore linter comments for this change.
Prefer single-quoted strings when you don't need string interpolation or special symbols.