Co-authored-by: Weston Ruter <westonruter@google.com>

Previously, the flags were set as if UTF-8 were conditionally present,
but in most cases the blog character set will be UTF-8 and so flipping
the logic makes it clearer that this is a "happy path" and also remove
some logic that isn't necessary most of the time.

I've reworded and combined the comment explaining the flags to be more
specific about whey they are needed, and removed some discussions
about encodings that I thought muddied the important details.