remove _nb_ext_conf from legacy env
_nb_ext_conf adds configuration that requires nb_conda_kernels,
which has been removed, preventing launch
@@ -23,7 +23,7 @@ class LegacyBinderDockerBuildPack(DockerBuildPack):
RUN conda install -yq conda>=4.3 && \
conda install -yq conda==4.4.11 && \
conda env update -n python3 -f /tmp/python3.frozen.yml && \
- conda remove -yq -n python3 nb_conda_kernels && \
+ conda remove -yq -n python3 nb_conda_kernels _nb_ext_conf && \
conda env update -n root -f /tmp/root.frozen.yml && \
/home/main/anaconda2/envs/python3/bin/ipython kernel install --sys-prefix && \
/home/main/anaconda2/bin/ipython kernel install --prefix=/home/main/anaconda2/envs/python3 && \
