bpo-39605: Remove a cast that causes a warning. (GH-18473)

Author: benjaminp

Objects/unicodeobject.c

@@ -3420,7 +3420,7 @@ PyUnicode_Decode(const char *s,
 
  /* Decode via the codec registry */
  buffer = NULL;
- if (PyBuffer_FillInfo(&info, NULL, (const void *)s, size, 1, PyBUF_FULL_RO) < 0)
+ if (PyBuffer_FillInfo(&info, NULL, (void *)s, size, 1, PyBUF_FULL_RO) < 0)
  goto onError;
  buffer = PyMemoryView_FromBuffer(&info);
  if (buffer == NULL)