Issue #15067: Remove reference to a rejected PEP.

Further explanation of the concept stands alone without this reference,
no need to potentially confuse people by bringing up a feature that
doesn't exist.

Doc/library/sqlite3.rst

@@ -727,9 +727,6 @@ use other Python types with SQLite, you must **adapt** them to one of the
 sqlite3 module's supported types for SQLite: one of NoneType, int, long, float,
 str, unicode, buffer.
 
-The :mod:`sqlite3` module uses Python object adaptation, as described in
-:pep:`246` for this.  The protocol to use is :class:`PrepareProtocol`.
-
 There are two ways to enable the :mod:`sqlite3` module to adapt a custom Python
 type to one of the supported ones.