Clean py_env

Author: gangliao

cmake/external/python.cmake

@@ -18,7 +18,7 @@ INCLUDE(python_module)
 FIND_PACKAGE(PythonInterp 2.7)
 FIND_PACKAGE(PythonLibs 2.7)
 
-SET(py_env PATH=${PATH} PYTHONHOME=${PYTHONHOME} PYTHONPATH=${PYTHONPATH})
+SET(py_env "")
 
 IF(PYTHONLIBS_FOUND AND PYTHONINTERP_FOUND)
     find_python_module(pip REQUIRED)