RFR: 8315580: Remove unused java_lang_String::set_value_raw()

[Albert Mingkun Yang]

On Sun, 3 Sep 2023 18:55:45 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this trivial change to remove the unused function java_lang_String::set_value_raw.
> 
> Testing:
> mach5 tier1

Marked as reviewed by ayang (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/15552#pullrequestreview-1613862500