Conspiracy theory: They actually only removed the "blackface" episodes as a smokescreen so they could memory hole the creepy Oprah episode [captioned screencap] [discussion]
Mainly how Liz and some other characters basically worships her. With the PR veil around her slowly being lifted, it would make sense to want to get out in front of the scandal and just pretend 30 Rock never idolized her in the first place.