Remove unused packaging/pkg_helpers.bash, Remove CONDA_CHANNEL_FLAGS (#7656)

Author: atalman

packaging/pkg_helpers.bash

@@ -13,7 +13,7 @@ fi
 
 if [[ "$(uname)" == Darwin || "$OSTYPE" == "msys" ]]; then
   # Install libpng from Anaconda (defaults)
-  conda install ${CONDA_CHANNEL_FLAGS} libpng "jpeg<=9b" -y
+  conda install libpng "jpeg<=9b" -yq
   conda install -yq ffmpeg=4.2 -c pytorch
 
   # Copy binaries to be included in the wheel distribution