Change register_* calls from hpx::applier to hpx::threads namespace

Author: msimberg

src/util/interval_timer.cpp

@@ -250,7 +250,7 @@ namespace hpx { namespace util { namespace detail
             // lock here would be the right thing but leads to crashes and hangs
             // at shutdown.
             //util::unlock_guard<std::unique_lock<mutex_type> > ul(l);
-            id = hpx::applier::register_thread_plain(
+            id = hpx::threads::register_thread_plain(
                 util::bind_front(&interval_timer::evaluate,
                     this->shared_from_this()),
                 description_.c_str(), threads::suspended, true,

src/util/one_size_heap_list.cpp

@@ -157,7 +157,7 @@ namespace hpx { namespace util
     {
         if (nullptr == threads::get_self_ptr())
         {
-            hpx::applier::register_work_nullary(
+            hpx::threads::register_work_nullary(
                 util::bind_front(&one_size_heap_list::free, this, p, count),
                 "one_size_heap_list::free");
             return true;