Remove set-hooks.h from generic includes

The hooks mechanism uses symbol sets for running lists of functions,
which requires either extra linker directives to provide any hardening
(such as RELRO) or additional code (such as pointer obfuscation via
mangling with random value).

Currently only hurd uses set-hooks.h so we remove it from the generic
includes.  The generic implementation uses direct function calls which
provide hardening and good code generation, observability and debugging
without the need for extra linking options or special code handling.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

diff --git a/include/set-hooks.h b/hurd/set-hooks.h
similarity index 100%
rename from include/set-hooks.h
rename to hurd/set-hooks.h