portmgr/policies_eol: Update supported branch

• Remove old unsupported releases from 13.X
• Remove old unsupported releases from 14.X
• Update stable/13 to point to releng/13.5
• Update stable/14 to point to releng/14.2. Although EOL we have not yet generated pkgs from 14.3. Will update once the pkgs are propagated
• Update main to point to FreeBSD:16 instead of FreeBSD:15
• Will add necessary branches once 15.0 is out

Approved by: portmgr (blanket)
Sponsored by: The FreeBSD Foundation