patch 8.2.0966: 'shortmess' flag "n" not used in two places

Problem:    'shortmess' flag "n" not used in two places.
Solution:   Make use of the "n" flag consistent. (Nick Jensen, closes #6245,
            closes #6244)
diff --git a/src/proto/bufwrite.pro b/src/proto/bufwrite.pro
index 5d7b4a2..72c08da 100644
--- a/src/proto/bufwrite.pro
+++ b/src/proto/bufwrite.pro
@@ -1,3 +1,4 @@
 /* bufwrite.c */
+char *new_file_message(void);
 int buf_write(buf_T *buf, char_u *fname, char_u *sfname, linenr_T start, linenr_T end, exarg_T *eap, int append, int forceit, int reset_changed, int filtering);
 /* vim: set ft=c : */