Delete outdated paragraph about OptimizedUnicode again

sqlite3.OptimizedUnicode is an alias for str in Python 3 and
its behavior is already tested in CheckOptimizedUnicode in
Lib/sqlite3/test/factory.py.

sqlite3.OptimizedUnicode was undocumented in 0fc10a33eb4c and
probably added back with the result of a bad merge.

Author: berkerpeksag

Doc/library/sqlite3.rst

@@ -489,10 +489,6 @@ Connection Objects
       :mod:`sqlite3` module will return Unicode objects for ``TEXT``. If you want to
       return bytestrings instead, you can set it to :class:`bytes`.
 
-      For efficiency reasons, there's also a way to return :class:`str` objects
-      only for non-ASCII data, and :class:`bytes` otherwise. To activate it, set
-      this attribute to :const:`sqlite3.OptimizedUnicode`.
-
       You can also set it to any other callable that accepts a single bytestring
       parameter and returns the resulting object.