RFR: 8254559: Remove unimplemented JVMFlag::get_locked_message_ext

[David Holmes]

On Mon, 12 Oct 2020 06:56:06 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> The definition was removed with JDK-8224599, the declaration was left behind.
> 
> Testing:
>  - [x] Linux x86_64 build
>  - [x] Text search for `get_locked_message_ext` in entire `src/`

Trivially good.

Thanks,
David

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Marked as reviewed by dholmes (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/598