PEP 630: Further revise and update to reflect reviewer input

Co-authored-by: Petr Viktorin <encukou@gmail.com>

pep-0630.rst

@@ -1,7 +1,7 @@
 PEP: 630
 Title: Isolating Extension Modules
 Author: Petr Viktorin <encukou@gmail.com>
-Discussions-To: https://mail.python.org/archives/list/capi-sig@python.org/
+Discussions-To: capi-sig@python.org
 Status: Active
 Type: Informational
 Content-Type: text/x-rst
@@ -345,10 +345,6 @@ the Python level: for example, you can't set ``str.myattribute = 123``.
    Thus, code that shares any Python objects across interpreters implicitly
    depends on CPython's current, process-wide GIL.
 
-   :pep:`683` proposes a mechanism to mark certain objects as
-   immortal, such that they will be truly immutable, though is is likewise
-   considered an internal implementation detail.
-
 Because they are immutable and process-global, static types cannot access
 "their" module state.
 If any method of such a type requires access to module state,
@@ -534,7 +530,7 @@ Slot methods -- the fast C equivalents for special methods, such as `nb_add
 for ``__add__`` or `tp_new
 <https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_new>`__
 for initialization -- have a very simple API that doesn't allow
-passing in the defining class, as is the case in ``PyCMethod``.
+passing in the defining class, unlike with ``PyCMethod``.
 The same goes for getters and setters defined with
 `PyGetSetDef <https://docs.python.org/3/c-api/structures.html#c.PyGetSetDef>`__.