rebase -i: remove duplication

path_state_dir() and merge_dir() refer to the same path so remove one of
them.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -37,7 +37,6 @@ static char const * const builtin_rebase_usage[] = {
 	NULL
 };
 
-static GIT_PATH_FUNC(path_state_dir, "rebase-merge/")
 static GIT_PATH_FUNC(path_squash_onto, "rebase-merge/squash-onto")
 static GIT_PATH_FUNC(path_interactive, "rebase-merge/interactive")
 static GIT_PATH_FUNC(apply_dir, "rebase-apply")
@@ -182,8 +181,8 @@ static int init_basic_state(struct replay_opts *opts, const char *head_name,
 {
 	FILE *interactive;
 
-	if (!is_directory(path_state_dir()) && mkdir_in_gitdir(path_state_dir()))
-		return error_errno(_("could not create temporary %s"), path_state_dir());
+	if (!is_directory(merge_dir()) && mkdir_in_gitdir(merge_dir()))
+		return error_errno(_("could not create temporary %s"), merge_dir());
 
 	delete_reflog("REBASE_HEAD");