[ConstraintSystem] Marking closure parameter as potentially incomplete is not longer necessary

Since closure body isn't opened until its contextual type is resolved
there is no need to explicitly delay attempting bindings for closure
parameter used in the body anymore.

Author: xedin

lib/Sema/CSBindings.cpp

@@ -972,20 +972,6 @@ bool ConstraintSystem::PotentialBindings::infer(
   case ConstraintKind::ArgumentConversion:
   case ConstraintKind::OperatorArgumentConversion:
   case ConstraintKind::OptionalObject: {
-    // If there is a `bind param` constraint associated with
-    // current type variable, result should be aware of that
-    // fact. Binding set might be incomplete until
-    // this constraint is resolved, because we currently don't
-    // look-through constraints expect to `subtype` to try and
-    // find related bindings.
-    // This only affects type variable that appears one the
-    // right-hand side of the `bind param` constraint and
-    // represents result type of the closure body, because
-    // left-hand side gets types from overload choices.
-    if (constraint->getKind() == ConstraintKind::BindParam &&
-        constraint->getSecondType()->isEqual(TypeVar))
-      PotentiallyIncomplete = true;
-
     auto binding =
         cs.getPotentialBindingForRelationalConstraint(*this, constraint);
     if (!binding)