cudf no longer links to arrow or pyarrow

[vyasr]

I noticed that legate still has some CMake copied over from cudf that we have since removed as part of removing our dependency on arrow. I don't know if legate is directly using pyarrow in Cython still; if so, we can close this issue. If not, then legate can probably clean out some things and simplify the build since cudf no longer requires arrow at build time.