RFR: 8302734: Parallel: Remove unused LGRPSpace::_invalid_region

[Thomas Schatzl]

On Fri, 17 Feb 2023 11:01:54 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Trivial removing dead code.

Lgtm + trivial.

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Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.org/jdk/pull/12615