commit.h: reduce unnecessary includes

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/archive.c b/archive.c
index ab8966d..6226e16 100644
--- a/archive.c
+++ b/archive.c
@@ -6,10 +6,12 @@
 #include "environment.h"
 #include "gettext.h"
 #include "hex.h"
+#include "pretty.h"
 #include "setup.h"
 #include "refs.h"
 #include "object-store.h"
 #include "commit.h"
+#include "tree.h"
 #include "tree-walk.h"
 #include "attr.h"
 #include "archive.h"