Remove set of submodule update `checkout_strategy`

Remove overriding the `checkout_strategy` for `update_options` when
performing an update on a submodule. Users should be specifying the
correct checkout strategy in
`update_options.checkout_opts.checkout_strategy`.

src/submodule.c

@@ -1160,7 +1160,6 @@ int git_submodule_update(git_submodule *sm, int init, git_submodule_update_optio
 		 * will checkout the specific commit manually.
 		 */
 		clone_options.checkout_opts.checkout_strategy = GIT_CHECKOUT_NONE;
-		update_options.checkout_opts.checkout_strategy = GIT_CHECKOUT_SAFE;
 
 		if ((error = git_clone(&sub_repo, submodule_url, sm->path, &clone_options)) < 0 ||
 			(error = git_repository_set_head_detached(sub_repo, git_submodule_index_id(sm))) < 0 ||