Remove Spack external find from startup

Spack was running an external detection of Python during each invocation
of the setup script for Windows CMD/PWSH, which has dramatic performance
implications each time the script is invoked, and is completely
unneccesary. Remove this operation.

bin/spack_cmd.bat

@@ -52,7 +52,6 @@ if defined py_path (
 
 if defined py_exe (
     "%py_exe%" "%SPACK_ROOT%\bin\haspywin.py"
-    "%py_exe%" "%SPACK_ROOT%\bin\spack" external find python >NUL
 )
 
 set "EDITOR=notepad"