gh-123909: Remove obsolete note in PyType_FromMetaclass

Docs of the other `PyType_From*` functions link to `PyType_FromMetaclass`,
which noted that they differ for backwards compatibility reasons.
The note is no longer relevant in 3.14.
The other functions have `versionchanged` blurbs.

Author: encukou

Doc/c-api/type.rst

@@ -311,10 +311,6 @@ The following functions and structs are used to create
 
    Metaclasses that override :c:member:`~PyTypeObject.tp_new` are not
    supported, except if ``tp_new`` is ``NULL``.
-   (For backwards compatibility, other ``PyType_From*`` functions allow
-   such metaclasses. They ignore ``tp_new``, which may result in incomplete
-   initialization. This is deprecated and in Python 3.14+ such metaclasses will
-   not be supported.)
 
    The *bases* argument can be used to specify base classes; it can either
    be only one class or a tuple of classes.