Replace conda-mambabuild with conda-build (#752)

These are now equivalent in behavior. However support for `conda-mambabuild` is being dropped. So switch to `conda-build`.

xref: rapidsai/build-planning#149

Authors:
  - https://github.com/jakirkham

Approvers:
  - James Lamb (https://github.com/jameslamb)

URL: #752

ci/build_python.sh

@@ -15,15 +15,13 @@ rapids-print-env
 
 rapids-logger "Build rapids-xgboost"
 
-rapids-conda-retry mambabuild \
-  --use-local \
+rapids-conda-retry build \
   --variant-config-files "${CONDA_CONFIG_FILE}" \
   conda/recipes/rapids-xgboost
 
 rapids-logger "Build rapids"
 
-rapids-conda-retry mambabuild \
-  --use-local \
+rapids-conda-retry build \
   --variant-config-files "${CONDA_CONFIG_FILE}" \
   conda/recipes/rapids