RFR: 8301098: Remove dead code FileMapInfo::stop_sharing_and_unmap()

[Ioi Lam]

On Wed, 25 Jan 2023 17:31:24 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Please review this trivial patch. The function `FileMapInfo::stop_sharing_and_unmap()` is no longer being used so it should be removed.
>
> Seems like a trivial change.

Thanks @coleenp and @calvinccheung for the review.

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PR: https://git.openjdk.org/jdk/pull/12205