home, sidebars, /releases/: updates, corrections

13.0 is end of life, 14.0-RELEASE is scheduled.

https://www.freebsd.org/releases/:

• whilst the legacy section is commented out, it makes no sense to distinguish between production and legacy
• do not misdirect readers to the Release Documentation page, which directs readers back to this page
• https://www.freebsd.org/security/unsupported/ is not a section, it's a separate page.

PR: 266094, 266167
Reviewed by: carlavilla, gjb (mentors)
Approved by: carlavilla (mentor)
Differential revision: https://reviews.freebsd.org/D36520