i18n: unmark a message in rebase.c

Commit v2.25.0-4-ge98c4269c8 (rebase (interactive-backend): fix handling
of commits that become empty, 2020-02-15) marked "{drop,keep,ask}" for
translation, but this message should not be changed.

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -1551,7 +1551,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 				 "ignoring them"),
 			      REBASE_PRESERVE_MERGES, PARSE_OPT_HIDDEN),
 		OPT_RERERE_AUTOUPDATE(&options.allow_rerere_autoupdate),
-		OPT_CALLBACK_F(0, "empty", &options, N_("{drop,keep,ask}"),
+		OPT_CALLBACK_F(0, "empty", &options, "{drop,keep,ask}",
 			       N_("how to handle commits that become empty"),
 			       PARSE_OPT_NONEG, parse_opt_empty),
 		{ OPTION_CALLBACK, 'k', "keep-empty", &options, NULL,