handbook/audit: fix internal xrefs

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Summary

Internal crossreferences in the FreeBSD handbook using crossref: are currently broken on PDF output. The official docs [0] say to use <<here-is-the-xref>>. Most links are already written with that notation, they are clean and they work great. Update the rest of the remaining xrefs in this chapter to this notation.

[0] : https://docs.asciidoctor.org/asciidoc/latest/macros/xref/

Related bug : https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=266107

Similar fix for bsdinstall : https://reviews.freebsd.org/D46262
Similar fix for basics : https://reviews.freebsd.org/D46260
Similar fix for advanced networking : https://reviews.freebsd.org/D46258

Test Plan

Links clicked on en/{html,pdf}

[concussious.bugzilla_runbox.com]

Removed redundant text

[fernape]

See https://reviews.freebsd.org/D46266#inline-277720 before working on this

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Closing: overcome by events: Fernape fixed the internal macro in D46480!