bpo-38096: Clean up the "struct sequence" / "named tuple" docs (GH-15895)

* bpo-38096: Clean up the "struct sequence" / "named tuple" docs

* Fix remaining occurrences of "struct sequence"

* Repair a user visible docstring
diff --git a/Objects/longobject.c b/Objects/longobject.c
index ed25e0b..6afec18 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -5780,7 +5780,7 @@
 PyDoc_STRVAR(int_info__doc__,
 "sys.int_info\n\
 \n\
-A struct sequence that holds information about Python's\n\
+A named tuple that holds information about Python's\n\
 internal representation of integers.  The attributes are read only.");
 
 static PyStructSequence_Field int_info_fields[] = {