prepare-root: Don't be strict about the sysroot mount name here

While the systemd integration effectively requires /sysroot, it will
help people trying to use OSTree with other initramfs systems
(e.g. initramfs-tools) if we don't hardcode that requirement in this
tool.

src/switchroot/ostree-prepare-root.c

@@ -100,11 +100,6 @@ main(int argc, char *argv[])
     }
 
   root_mountpoint = argv[1];
-  if (strcmp (root_mountpoint, "/sysroot") != 0)
-    {
-      fprintf (stderr, "ostree-prepare-root: Expected /sysroot\n");
-      exit (1);
-    }
 
   ostree_target = parse_ostree_cmdline ();
   if (!ostree_target)