repo: Flip the fsync default to off for new checkout API

Since we're adding a new API, we have the opportunity to fix
the defaults.  We expect clients to do a `syncfs()` or equivalent
on their own now, since it's way more efficient.

Flip the checkout fsync default to off.

Closes: #425
Approved by: giuseppe

src/libostree/ostree-sysroot-deploy.c

@@ -554,11 +554,6 @@ checkout_deployment_tree (OstreeSysroot     *sysroot,
   glnx_fd_close int osdeploy_dfd = -1;
   int ret_fd;
 
-  /* We end up using syncfs for the entire filesystem, so turn off
-   * OstreeRepo level fsync.
-   */
-  checkout_opts.disable_fsync = TRUE;
-
   osdeploy_path = g_strconcat ("ostree/deploy/", ostree_deployment_get_osname (deployment), "/deploy", NULL);
   checkout_target_name = g_strdup_printf ("%s.%d", csum, ostree_deployment_get_deployserial (deployment));