It makes some sense to remove the term slave since it's a direct reference to slavery and there are a bunch of other terms that you can use which won't be offensive and will also be more descriptive and professional. Master on the other hand has multiple different uses and meanings most of which have nothing to do with slavery. Changing the naming of git branches seems like a massive overreaction, doesn't achieve anything substantial and it also sets a strange precedent in which one use case of a word damages all others.