object-store: merge "object-store-ll.h" and "object-store.h"

The "object-store-ll.h" header has been introduced to keep transitive
header dependendcies and compile times at bay. Now that we have created
a new "object-store.c" file though we can easily move the last remaining
additional bit of "object-store.h", the `odb_path_map`, out of the
header.

Do so. As the "object-store.h" header is now equivalent to its low-level
alternative we drop the latter and inline it into the former.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/unpack-trees.c b/unpack-trees.c
index cf5b73c..471837f 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -26,7 +26,7 @@
 #include "symlinks.h"
 #include "trace2.h"
 #include "fsmonitor.h"
-#include "object-store-ll.h"
+#include "object-store.h"
 #include "promisor-remote.h"
 #include "entry.h"
 #include "parallel-checkout.h"