submodule.h: drop declaration of connect_work_tree_and_git_dir

The function connect_work_tree_and_git_dir is declared in both submodule.h
and dir.h, such that one of them is redundant. As the function is
implemented in dir.c, drop the declaration from submodule.h

Signed-off-by: Stefan Beller <sbeller@google.com>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule.h

@@ -105,7 +105,6 @@ extern int push_unpushed_submodules(struct oid_array *commits,
 				    const char **refspec, int refspec_nr,
 				    const struct string_list *push_options,
 				    int dry_run);
-extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir);
 /*
  * Given a submodule path (as in the index), return the repository
  * path of that submodule in 'buf'. Return -1 on error or when the