[FIX] Fix import syntax to enable shutil.which check

In PR 1585 a syntax error was introduced  as `shutil.which` is a method of the Python
'shutil' module and not a module, so the proper import is `from shutil import which`
as regardless of the CPython version `import shutil.which` will result in a

ModuleNotFoundError: No module named 'shutil.which'; 'shutil' is not a package

This error was causing all runs of packaging/wheel/install.sh to use the legacy behavior
of `python setup.py install` regardless if `shutil.which` was available or not.

packaging/wheel/install.sh

@@ -40,7 +40,7 @@ fi
 cd ../bindings/python
 
 # Determine if shutil.which is available for a modern Python package install
-${6} -c 'import shutil.which' &> /dev/null  # $6 holds the python sys.executable
+${6} -c 'from shutil import which' &> /dev/null  # $6 holds the python sys.executable
 shutil_which_available=$?
 if [ "${shutil_which_available}" -ne "0" ]; then
     ${6} setup.py install ${3}