This change was made after exploring turning this into a permission. It occurred to me that this feature is entirely superfluous because it's non-vanilla, can be done by plugins, and is usually considered as a bug. In addition, disabling this behaviour required third party code just for this one thing because it was not able to be managed by a permissions plugin.
Instead, it's better to produce a plugin which implements this behaviour if it's desired, by making use of SignChangeEvent and PlayerChatEvent/PlayerCommandPreprocessEvent.
close#3856, close#2288
