To be specific, the edit in question replaced <references responsive /> with <references />. In response to community request (T173176), the default references style on enwiki was changed to responsive. Both <references /> and <references responsive /> produce the same output on enwiki. The tag was added by the first editor before responsive became the default style, so back then it did actually change the output. The tag was removed because it is redundant, and produces no change in output. This is intended.