Revert "[gitlab-ci] conda install conda-build from bdt environment into base [ci skip]"

This reverts commit accc66bc.

bob/devtools/data/gitlab-ci/single-package.yaml

@@ -26,9 +26,9 @@ stages:
     - curl --silent "${BOOTSTRAP}" --output "bootstrap.py"
     - python3 bootstrap.py -vv channel bdt
     - source ${CONDA_ROOT}/etc/profile.d/conda.sh
-    - conda activate bdt
     # for conda inspect during builds (on macos)
     - conda install -n base conda-build
+    - conda activate bdt
     - bdt ci check -vv
   cache:
     paths: