Why remove it? Why break everyone when you can just deprecate it indefinitely or at least for a very long time?
Deprecated it, write clear warning messages with links to official docs, suggesting alternatives. Update official docs to reflect the idioms. Done.
PHP as a language and ecosystem seems to be evolving backwards from a reliable, productive and accessible tool to something that is breaking callers, introduces versioning and upgrade issues.
And it's already harder to debug than competing languages, because errors are spread across the server, the language runtime and even within that there's different types of error systems with error reporting, exceptions, error values and so on.
I'm impressed by some of the improvements that PHP went through and there are some rock solid tools and libraries (the star here is composer) but at the same time I feel less and less confident using it from a stability perspective.