RFR: Use relevant variables in log messages, remove unused import

[Kelvin Nilsen]

On Wed, 8 Mar 2023 22:03:01 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Addresses feedback in PR#220.

Marked as reviewed by kdnilsen (Committer).

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PR: https://git.openjdk.org/shenandoah/pull/222