RFR: 8356756: Cleanup: Make ClassLoaderData::_deallocate_list an object

[Coleen Phillimore]

On Thu, 8 May 2025 12:08:31 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> A small cleanup in order to get rid of some branches checking for null.
> 
> Testing: GHA

Most CLD won't have a deallocate list, so why do this?  It wastes another word per entry.

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PR Review: https://git.openjdk.org/jdk/pull/25117#pullrequestreview-2832964909