vim-patch:7.4.1731 Mark as NA

Leave a note in vim_diff.txt about it.

runtime/doc/vim_diff.txt

@@ -235,7 +235,7 @@ Additional differences:
 These legacy Vim features may be implemented in the future, but they are not
 planned for the current milestone.
 
-- vim.bindeval() (new feature in Vim 7.4 Python interface)
+- |if_py|: vim.bindeval() and vim.Function() are not supported
 - |if_lua|
 - |if_perl|
 - |if_mzscheme|

src/nvim/version.c

@@ -710,7 +710,7 @@ static int included_patches[] = {
   1734,
   // 1733 NA
   1732,
-  // 1731,
+  // 1731 NA
   1730,
   // 1729 NA
   1728,