Revert "[CSBindings] Mark generic parameter type vars as complete if they don't have any adjacent vars"

This reverts commit 22e0f4a.

Resolves: rdar://135203192

Author: xedin

lib/Sema/CSBindings.cpp

@@ -174,30 +174,9 @@ bool BindingSet::involvesTypeVariables() const {
 }
 
 bool BindingSet::isPotentiallyIncomplete() const {
-  // Always marking generic parameter type variables as incomplete
-  // is too aggressive. That was the way to make sure that they
-  // are never attempted to eagerly, but really there are only a
-  // couple of situations where that can cause issues:
-  //
-  // 1. Int <: $T_param
-  //    $T1 <: $T_param
-  //
-  // 2. $T2 conv Generic<$T_param>
-  //    $T2 conv Generic<Int?>
-  //    Int <: $T_param
-  //
-  // Attempting $T_param before $T1 in 1. could result in a missed
-  // optional type binding for example.
-  //
-  // Attempting $T_param too early in this case (before $T2) could
-  // miss some transitive bindings inferred through conversion
-  // of `Generic` type.
-  //
-  // If a type variable that represents a generic parameter is no longer
-  // associated with any type variables (directly or indirectly) it's safe
-  // to assume that its binding set is complete.
+  // Generic parameters are always potentially incomplete.
   if (Info.isGenericParameter())
-    return involvesTypeVariables();
+    return true;
 
   // Key path literal type is incomplete until there is a
   // contextual type or key path is resolved enough to infer