Fix a regression when a type method like ``__init__()`` is modified in a
subinterpreter. Fix a regression in ``_PyUnicode_EqualToASCIIId()`` and type
``update_slot()``. Revert the change which made the Unicode dictionary of
interned strings compatible with subinterpreters: the internal interned
dictionary is shared again by all interpreters. Patch by Victor Stinner.