Are there any famous rishonim or achronim (outside of Yemen & besides the Rambam) who hold doing chalita to meat is necessary?
The Sephardim who performed chalita don't do it anymore based on scientific basis. The machloket for hundreds of years was wether chalita was a requirement for kashering meat or it did the opposite and rendered it non-kosher. Science shows that chalita makes it impossible to ever kasher the meat. So to answer your question, nobody nowadays practices chalita