Not just C, but also BCPL.
So, they yanked out all the ASM, redid the C stuff to deal with differences in cpu arch, pulled the BCPL...
There really isn't a whole lot left...
The BCPL stuff was mostly down to dos.library and it's TripOS heritage, if I recall. I don't think there was a great deal of TripOS code in it but remnants such as BPTR stem from it. The dos.library required a total rewrite for OS4 anyway.
