environment: move object database functions into object layer

The `odb_mkstemp()` and `odb_pack_keep()` functions are quite clearly
tied to the object store, but regardless of that they are located in
"environment.c". Move them over, which also helps to get rid of
dependencies on `the_repository` in the environment subsystem.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bundle-uri.c

@@ -4,7 +4,6 @@
 #include "bundle-uri.h"
 #include "bundle.h"
 #include "copy.h"
-#include "environment.h"
 #include "gettext.h"
 #include "refs.h"
 #include "run-command.h"
@@ -13,6 +12,7 @@
 #include "config.h"
 #include "fetch-pack.h"
 #include "remote.h"
+#include "object-store-ll.h"
 
 static struct {
 	enum bundle_list_heuristic heuristic;