[CSClosure] NFC: Remove outdated FIXME about SolutionApplicationTarget

Author: xedin

lib/Sema/CSClosure.cpp

@@ -833,7 +833,6 @@ class ClosureConstraintGenerator
                                      contextualTy,
                                      /*isDiscarded=*/false);
 
-    // FIXME: Use SolutionApplicationTarget?
     if (cs.generateConstraints(target, FreeTypeVariableBinding::Disallow)) {
       hadError = true;
       return;