ENH: version.py seems to not require datetime import any longer

so to avoid change of file while doing setup.py, removing pasting of the import
of datetime into version.py

Author: yarikoptic

setup.py

@@ -135,8 +135,6 @@
 
 def write_version_py(filename='pandas/version.py'):
     cnt = """\
-from datetime import datetime
-
 version = '%s'
 """
     a = open(filename, 'w')