We no longer wrap section headings in a `\hypertarget`.
This is unnecessary (hyperref creates an anchor based on the
label) and it interferes with tagging.
In addition, we now use `\hyperref` rather than `\hyperlink`
for internal links.
Currently `\hypertarget` is still being used for link anchors
not on headings.
Closes#8744. Thanks to @u-fischer.
John MacFarlane