Remove CommandSpec.from_param test using sys.executable.
Remove CommandSpec.from_param test using sys.executable.

It was based on the assumption that CommandSpec.from_param(sys.executable)
should always return a 1-element list. Since from_param parses the argument
and sys.executable may contain unquoted spaces, this simply can't be
guaranteed.

pypa/setuptools,pypa/setuptools,pypa/setuptools