freebsd dockerfile: cleanup flavors

Version handling:

• python3.9 is the current default
  • explicitely add @py39 (not really necessary, but probably a good sanity check)
• net/pcl-smbclient: ensure we use the php82 version
• graphics/ImageMagcik: switch to 7, and don't add the X11 dependency
• graphics/librsvg2-rust: graphics/librsvg2 is for the rust is evil crowd and outdated
• editors/vim: only install the @console flavor

Additionally:

• editors/nano: added as requested some time ago in irc.