Accepting ":" in addition to "," seems confusing and dumb. It only
causing problems when you want to pass a value that contains ":". Remove
support for ":", it is now treated like any other normal character. This
affects all options that are listed as "Key/value list" in the option
list.
It's possible that this breaks for someone who happened to use ":" as
separator. But this was undocumented, and never recommended. Originally,
the option treated many other characters in a special way, but this was
changed in commit a3d561f950. I'm, not sure why ":" was explicitly
included. Maybe because -the absurd -vf/--af syntax uses ":" as list
separator. But "," was always recommended and used in examples for
key/value options.
Fixes: #8021 (if you consider it a bug)