Mostly, I don't think these changes should be made, particularly in cases where "slave" isn't mentioned at all.  The word "master" is used in many contexts where master/slave doesn't apply (such as "master key").   Also, I think the PR disrespects all the original authors of the various documentation entries, none of whom have been consulted.

If a particular passage is demonstrably unclear or offensive, it should be changed; otherwise, we shouldn't let vaguely formed notions of political correctness shape other clear uses of plain English.  

As far as I can't tell there isn't a single instance where the docs use "master" as a reference to human slavery or where the use could be seen to imply an endorsement of that notion.

FWIW, Guido drew a line for this a few years ago when someone suggested removing the example using the phrase, "I see said the blind man and he picked up the hammer and saw".  The judgment was that we weren't going to go down this path unless there was actual offensive speech.