The refref assignment is deleted

This avoids the most common dangling issue. Commented out test and todo
complete.

Author: steve-downey

src/Beman/Optional26/tests/optional_ref.t.cpp

@@ -613,12 +613,6 @@ TEST(OptionalRefTest, AssignFromOptional) {
     derived d2(2, 2);
     engaged_derived = d2;
     EXPECT_EQ(optional_base_ref.value().m_i, static_cast<base>(d2).m_i);
-
-    // delete the rvalue ref overload
-    // optional_base_const_ref = beman::optional26::optional<derived>(derived(3, 4));
-    // EXPECT_TRUE(optional_base_ref.has_value());
-    // EXPECT_EQ(*optional_base_ref, derived(3,4));
-
 }
 
 TEST(OptionalRefTest, ConstructFromOptional) {