message: Fix build on Clang 10
diff: @@ -339,7 +339,7 @@ public:
  }
  expect_clause& to(const caf::scoped_actor& whom) {
  - dest_ = whom.ptr();
  + dest_ = caf::actor_cast<caf::abstract_actor*>(whom);
  return *this;
  }
  @@ -415,7 +415,7 @@ public:
  }
  expect_clause& to(const caf::scoped_actor& whom) {
  - dest_ = whom.ptr();
  + dest_ = caf::actor_cast<caf::abstract_actor*>(whom);
  return *this;
  }
  @@ -455,11 +455,6 @@ public:
  return *this;
  }
  - inject_clause& to(const caf::scoped_actor& whom) {
  - dest_ = caf::actor_cast<caf::strong_actor_ptr>(whom.ptr());
  - return *this;
  - }
  -
  void with(Ts... xs) {
  if (dest_ == nullptr)
  CAF_FAIL("missing .to() in inject() statement");
  @@ -534,11 +529,6 @@ public:
  return *this;
  }
  - allow_clause& to(const caf::scoped_actor& whom) {
  - dest_ = whom.ptr();
  - return *this;
  - }
  -
  template <class... Us>
  void with(Us&&... xs) {
  // TODO: replace this workaround with make_tuple() when dropping support
  