Documentation: dontdiff: remove 'utf8data.h'

Commit 2b3d0478 ("unicode: Add utf8-data module") changed the
database file from 'utf8data.h' to 'utf8data.c' to build separate
module, but it seems forgot to update Documentation/dontdiff. Remove
'utf8data.h' and add 'utf8data.c'.
Signed-off-by: ganjie <ganjie5@huawei.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240808085707.3235019-1-guoxuenan@huawei.com

Documentation/dontdiff

@@ -262,7 +262,7 @@ vsyscall_32.lds
 wanxlfw.inc
 uImage
 unifdef
-utf8data.h
+utf8data.c
 wakeup.bin
 wakeup.elf
 wakeup.lds