* libguile/root.h:
* libguile/root.c: Remove these files.
* libguile/deprecated.h:
* libguile/deprecated.c (scm_internal_cwdr, scm_call_with_dynamic_root)
  (scm_dynamic_root, scm_apply_with_dynamic_root): Deprecate.

Remove all root.h usage, which was vestigial.

* module/ice-9/serialize.scm: Use (current-thread) instead
  of (dynamic-root).