This either became dead shortly after the removal of Swift 3
compatibility mode from the constraint solver, or even earlier.
Note that the code completion test change is actually correct
because (Any) -> () is not convertible to () -> () in the
language.
Since constraint solver has been improved to diagnose more problems
via "fixes", sometimes applying fixes might lead to producing solutions
which are completely ambiguous when compared to each other, and/or are
incomparable, which leads to `findBestSolutions` erasing all of them
while trying to compute best "partial" solution, which is incorrect.
Resolves: rdar://problem/42678836