Drop --use-local as it is implied

The default behavior of `conda-build` is to use packages from its local
cache. Given this, we don't need this flag. It also causes conda-build
to look in a different place than we typically use for the package cache
on CI, which causes its own problems.

ci/build_python.sh

@@ -16,14 +16,12 @@ rapids-print-env
 rapids-logger "Build rapids-xgboost"
 
 rapids-conda-retry build \
-  --use-local \
   --variant-config-files "${CONDA_CONFIG_FILE}" \
   conda/recipes/rapids-xgboost
 
 rapids-logger "Build rapids"
 
 rapids-conda-retry build \
-  --use-local \
   --variant-config-files "${CONDA_CONFIG_FILE}" \
   conda/recipes/rapids