bpo-40182: Remove the _field_types attribute of the NamedTuple class (GH-19368)

diff --git a/Lib/typing.py b/Lib/typing.py
index 99355d0..a72003a 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1705,9 +1705,7 @@
     msg = "NamedTuple('Name', [(f0, t0), (f1, t1), ...]); each t must be a type"
     types = [(n, _type_check(t, msg)) for n, t in types]
     nm_tpl = collections.namedtuple(name, [n for n, t in types])
-    # Prior to PEP 526, only _field_types attribute was assigned.
-    # Now __annotations__ are used and _field_types is deprecated (remove in 3.9)
-    nm_tpl.__annotations__ = nm_tpl._field_types = dict(types)
+    nm_tpl.__annotations__ = dict(types)
     try:
         nm_tpl.__module__ = sys._getframe(2).f_globals.get('__name__', '__main__')
     except (AttributeError, ValueError):
@@ -1717,7 +1715,7 @@
 
 # attributes prohibited to set in NamedTuple class syntax
 _prohibited = {'__new__', '__init__', '__slots__', '__getnewargs__',
-               '_fields', '_field_defaults', '_field_types',
+               '_fields', '_field_defaults',
                '_make', '_replace', '_asdict', '_source'}
 
 _special = {'__module__', '__name__', '__annotations__'}