Revert "[CSBindings] Mark type variables that represent packs as involving type variables"

This reverts commit 8a39f3f.

Author: xedin

lib/Sema/CSBindings.cpp

@@ -148,11 +148,6 @@ bool BindingSet::isDelayed() const {
 }
 
 bool BindingSet::involvesTypeVariables() const {
-  // This type variable always depends on a pack expansion variable
-  // which should be inferred first if possible.
-  if (TypeVar->getImpl().canBindToPack())
-    return true;
-
   // This is effectively O(1) right now since bindings are re-computed
   // on each step of the solver, but once bindings are computed
   // incrementally it becomes more important to double-check that