builtin/stash: remove unused header

Clang complains that oid-array.h is unused. Certainly none of the
oid_array* functions, types, etc., are used, and the
transitively-included hash.h declarations are used but covered by a
pre-existing direct #include of hash.h.

Signed-off-by: D. Ben Knoble <ben.knoble@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/stash.c

@@ -31,7 +31,6 @@
 #include "reflog.h"
 #include "reflog-walk.h"
 #include "add-interactive.h"
-#include "oid-array.h"
 #include "commit.h"
 
 #define INCLUDE_ALL_FILES 2