RFR: 8325551: Remove unused obj_is_alive and block_start in Space [v2]

[Stefan Karlsson]

On Fri, 9 Feb 2024 13:10:16 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Trivial removing dead code.
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

Marked as reviewed by stefank (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17786#pullrequestreview-1872587080