try removing the upstream-dev build of pyarrow [skip-ci][skip-rtd]

Supposedly `pyarrow>=16.0` is compatible with `numpy>=2`, but I don't
know whether the version on `conda-forge` is built against the release
candidate of `numpy`.

ci/install-upstream-wheels.sh

@@ -30,15 +30,6 @@ python -m pip install \
     matplotlib \
     pandas \
     h5py
-# for some reason pandas depends on pyarrow already.
-# Remove once a `pyarrow` version compiled with `numpy>=2.0` is on `conda-forge`
-python -m pip install \
-    -i https://pypi.fury.io/arrow-nightlies/ \
-    --prefer-binary \
-    --no-deps \
-    --pre \
-    --upgrade \
-    pyarrow
 python -m pip install \
     --no-deps \
     --upgrade \