12.4 release notes: sshd precaution, empty section

[grahamperrin]

Summary

From FreeBSD bug 268199:

Given bug 263489 comment 23, I imagine that there was an omission from release notes for 12.4.

Whilst here, hide an empty section and subsection.

Origin of this diff:

• https://github.com/freebsd/freebsd-doc/compare/main...grahamperrin:freebsd-doc:releng/12.4.diff.

Test Plan

Preview in GitHub:

• https://github.com/grahamperrin/freebsd-doc/blob/releng/12.4/website/content/en/releases/12.4R/relnotes.adoc#upgrading-from-previous-releases-of-freebsd.

[grahamperrin]

OpenSSH service broken upgrading from 12.3 to 12.4 : freebsd – I'll pin this as an announcement for a few weeks.