[review] consider removing reference collapsing logic

[badair]

"reference collapsing" behavior on the add ref-qualifier traits is subtle and arbitrary and I'm not aware of use cases calling for such rules. The FAQ's argument - that a different set of rules would be
hard to memorize - does not sound very convincing to me. It sounds like the problem came from the name of the trait: "adding" a && qualifier to a &-qualified function type doesn't make much sense. If,
say, the name is recast as "make the function type && qualified", then the behavior would be obvious.

from http://lists.boost.org/Archives/boost/2017/04/234173.php

[badair]

Good suggestion, but closing as won't fix.