Remove Dbm.

Demo/classes/README

@@ -2,7 +2,6 @@ Examples of classes that implement special operators (see reference manual):
 
 Complex.py	Complex numbers
 Dates.py	Date manipulation package by Tim Peters
-Dbm.py		Wrapper around built-in dbm, supporting	arbitrary values
 Range.py	Example of a generator: re-implement built-in range()
 Rev.py		Yield the reverse of a sequence
 Vec.py		A simple vector class