I'm not sure what you could remove and have it not change the plot (barring actually changing the story) and character development. Finn needs the whole child/animal slave part to put a face on the thing the resistance is fighting for, they need to find a code breaker, they need to get back on the Supremacy, Finn needs to see that being neutral isn't really an option for him (that's the whole point of DJ, to be a foil to Rose's belief in the mission of the Resistance). I get why people don't like Canto Bight, but the whole sequence is pretty important to Finn's character development and the overall plot (if they don't make it on the Supremacy, the resistance makes it to Crait safely and has time to wait for an ally to come).