remove case_sensitive create_engine parameter

remove case_sensitive create_engine parameter

Removed the previously deprecated ``case_sensitive`` parameter from
:func:`_sa.create_engine`, which would impact only the lookup of string
column names in Core-only result set rows; it had no effect on the behavior
of the ORM. The effective behavior of what ``case_sensitive`` refers
towards remains at its default value of ``True``, meaning that string names
looked up in ``row._mapping`` will match case-sensitively, just like any
other Python mapping.

Change-Id: I0dc4be3fac37d30202b1603db26fa10a110b618d