Remove recommendation of the Aikars flags

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The Aikars flags are old and outdated. Using them on Java 17 and 21 does users a massive disservice, as they are built around the archaic G1 garbage collector. Shenandoah on Java 17 and Generational ZGC on Java 21 are significantly more performant, with GenZGC providing sub-millisecond maximum GC pauses.