[Type checker] Eliminate generation of useless constraints NFC.

There's no point in adding the constraints known on an associated type
to the constraint system, because they're implied by the protocol
constraint itself.

Author: DougGregor

lib/Sema/ConstraintSystem.cpp

@@ -468,25 +468,6 @@ namespace {
                                             FunctionRefKind::Compound,
                                             locator));
 
-        if (!archetype) {
-          // If the nested type is not an archetype (because it was constrained
-          // to a concrete type by a requirement), return the fresh type
-          // variable now, and let binding occur during overload resolution.
-          return memberTypeVar;
-        }
-                                
-        // FIXME: Would be better to walk the requirements of the protocol
-        // of which the associated type is a member.
-        if (auto superclass = member->getSuperclass()) {
-          CS.addConstraint(ConstraintKind::Subtype, memberTypeVar,
-                           superclass, locator);
-        }
-
-        for (auto proto : member->getConformingProtocols()) {
-          CS.addConstraint(ConstraintKind::ConformsTo, memberTypeVar,
-                           proto->getDeclaredType(), locator);
-        }
-
         return memberTypeVar;
       });
     }