RFR: 8253348: Remove unimplemented JNIHandles::initialize

[Zhengyu Gu]

On Fri, 18 Sep 2020 10:45:16 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Seems to be a left-over from JDK-8227053 that removed the definition, but left the declaration behind.
> 
> Testing:
>   - [x] Linux x86_64 fastdebug build
>   - [x] Text search for `JNIHandles::initialize` in `src/hotspot`

Looks good and trivial

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Marked as reviewed by zgu (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/243