gh-112636: remove check for float subclasses without nb_float

Misc/NEWS.d/next/C_API/2024-10-01-14-53-55.gh-issue-112636.t4WJjC.rst

@@ -0,0 +1,4 @@
+:c:func:`PyNumber_Float` doesn't fallback anymore to
+``PyFloat_FromDouble(PyFloat_AS_DOUBLE(obj))`` if a :class:`float` subtype resets
+:c:member:`~PyNumberMethods.nb_float` to ``NULL``.  A :exc:`TypeError`
+exception is raised instead.

Objects/abstract.c

@@ -1638,10 +1638,6 @@ PyNumber_Float(PyObject *o)
         return PyFloat_FromDouble(val);
     }
 
-    /* A float subclass with nb_float == NULL */
-    if (PyFloat_Check(o)) {
-        return PyFloat_FromDouble(PyFloat_AS_DOUBLE(o));
-    }
     return PyFloat_FromString(o);
 }