Remove dead code forgotten in previous commit.

notebook/_version.py

@@ -11,14 +11,3 @@ store the current version info of the notebook.
 
 version_info = (4, 1, 0, 'b1')
 __version__ = '.'.join(map(str, version_info[:3])) + ''.join(version_info[3:])
-
-import re
-
-pep440re = re.compile('^(\d+)\.(\d+)\.(\d+((a|b|rc)\d+)?)(\.post\d+)?(\.dev\d+)?$')
-
-def raise_on_bad_version(version):
-    if not pep440re.match(version):
-        raise ValueError("Versions String does apparently not match Pep 440 specification, "
-                         "which might lead to sdist and wheel being seen as 2 different release. "
-                         "E.g: do not use dots for beta/alpha/rc markers.")
-