In actionview, eliminate calls to tag that use html_safe parameter values.

This saves us calls to html_safe and lets `tag` decide how to escape characters.

My motivation here is that there is no need for anyone to attempt to HTML-encode strings before passing them as tag values, since:

1. Your code should have access to the actual string value of any parameter, not the encoded version.
2. You should not care about the exact encoding as HTML.
3. Thinking about how to safely encode strings is hard, and `tag` already does a fine job.

I would like to fix the few places where Rails itself does this, so that I can more easily verify during testing that my own code does not do this.

**Update:** I used an explicit HTML string in `utf8_enforcer_tag` due to concerns about document character encoding and eliminated the other two places in `actionview` where this was happening.
Why this was removed?