xen/xenstore: remove unused functions
Those helpers are not used, so remove them. No functional change.
Sponsored by: Citrix Systems R&D
MFC after: 3 days
(cherry picked from commit 2ae75536d370c238f77ad09e5e994d2b8bdf010c)
(cherry picked from commit af4ed05c3dd25c957b657f92f953bd9f00f818a8)
Approved by: so