You'll need to remove every instance of the two corresponding two zombies ("zombieScared" and "zombieCuriousGeorge") from the spawn lists.
You could also simply change the probabilities to 0.
(e.g. in entitygroups.xml, change
<entity name="zombieScared" prob="0.05"/>
<entity name="zombieCuriousGeorge" prob="0.01"/>
to
<entity name="zombieScared" prob="0"/>
<entity name="zombieCuriousGeorge" prob="0"/>
You'll want to use an editor and search function, and there are multiple occurrences.
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Also, if I'm haven't said as much earlier, I'm already enjoying 3.0 more than 2.2. Thanks for your work, Jax.