[ContraintSystem] Don't de-duplicate generic requirements

Looks like this is not really needed since fixed requirements
cache can handle such de-duplication.

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -126,33 +126,6 @@ void ConstraintSystem::mergeEquivalenceClasses(TypeVariableType *typeVar1,
   // Merge nodes in the constraint graph.
   CG.mergeNodes(typeVar1, typeVar2);
 
-  // Let's try to de-duplicate any generic requirements
-  // associated with given type variable, if it represents
-  // a generic parameter.
-  if (typeVar1->getImpl().getGenericParameter()) {
-    auto requirements = CG.gatherConstraints(
-        typeVar1, ConstraintGraph::GatheringKind::EquivalenceClass,
-        [](Constraint *constraint) -> bool {
-          if (auto *locator = constraint->getLocator()) {
-            return locator->isLastElement(
-                       ConstraintLocator::TypeParameterRequirement) ||
-                   locator->isLastElement(
-                       ConstraintLocator::ConditionalRequirement);
-          }
-
-          return false;
-        });
-
-    llvm::SmallPtrSet<TypeBase *, 4> existingRequirements;
-    for (auto *req : requirements) {
-      auto constraintTy = req->getSecondType();
-      // If this constraint has already been recorded in the
-      // constraint system, there is no reason to check it twice.
-      if (!existingRequirements.insert(constraintTy.getPointer()).second)
-        retireConstraint(req);
-    }
-  }
-
   if (updateWorkList) {
     addTypeVariableConstraintsToWorkList(typeVar1);
   }

lib/Sema/ConstraintSystem.h

@@ -637,8 +637,6 @@ class Solution {
   /// The list of member references which couldn't be resolved,
   /// and had to be assumed based on their use.
   llvm::SmallVector<ConstraintLocator *, 4> MissingMembers;
-  llvm::SmallVector<std::pair<GenericSignature *, unsigned>, 4>
-      FixedRequirements;
 
   /// The set of disjunction choices used to arrive at this solution,
   /// which informs constraint application.