gh-133260: Remove claim that PyUnicode_InternFromString immortalizes (GH-134213)

Author: encukou

Doc/c-api/unicode.rst

@@ -1726,10 +1726,6 @@ They all return ``NULL`` or ``-1`` if an exception occurs.
    from user input, prefer calling :c:func:`PyUnicode_FromString` and
    :c:func:`PyUnicode_InternInPlace` directly.
 
-   .. impl-detail::
-
-      Strings interned this way are made :term:`immortal`.
-
 
 .. c:function:: unsigned int PyUnicode_CHECK_INTERNED(PyObject *str)