(Bug 5113) Remove talkread/talkpost

This also adds a Carp::confess or next to two codepaths that would
refer to talkread.bml directly. Those shouldn't be in use on
Dreamwidth, but we handle them to preserve the flow of the code.

Also, the text files are not removed yet as those strings are still
referenced in a number of places.

Finally, the talkpost_do.bml page is still used by the preview system,
so that's left in still.