bpo-37151: remove _PyCFunction_FastCallDict (GH-14269)

diff --git a/Tools/gdb/libpython.py b/Tools/gdb/libpython.py
index 93f720a..abfea96 100755
--- a/Tools/gdb/libpython.py
+++ b/Tools/gdb/libpython.py
@@ -1563,8 +1563,7 @@
         if not caller:
             return False
 
-        if caller in ('_PyCFunction_FastCallDict',
-                      '_PyCFunction_Vectorcall',
+        if caller in ('_PyCFunction_Vectorcall',
                       'cfunction_call_varargs'):
             arg_name = 'func'
             # Within that frame: