histedit: don't bother with cPickle, demand-load pickle

We're unlikely to ever need the pickle module, so there's no good
reason to force loading of its faster cousin.

hgext/histedit.py

@@ -169,11 +169,7 b' the drop to be implicit for missing comm'
 
 """
 
-try:
-    import cPickle as pickle
-    pickle.dump # import now
-except ImportError:
-    import pickle
+import pickle
 import errno
 import os
 import sys