Revert "AST: Fix excessive deserialization in GenericSignatureBuilder"

Author: jrose-apple

lib/AST/GenericSignatureBuilder.cpp

@@ -554,16 +554,7 @@ auto GenericSignatureBuilder::PotentialArchetype::getNestedType(
   SmallVector<std::pair<ProtocolDecl *, RequirementSource>, 4>
     conformsTo(rep->ConformsTo.begin(), rep->ConformsTo.end());
   for (auto &conforms : conformsTo) {
-    // Make sure we don't trigger deserialization of extensions,
-    // since they can refer back to a protocol we're currently
-    // type checking.
-    //
-    // Note that typealiases in extensions won't matter here,
-    // because a typealias is never going to be a representative
-    // PA.
-    auto members = conforms.first->lookupDirect(nestedName,
-                                                /*ignoreNewExtensions=*/true);
-    for (auto member : members) {
+    for (auto member : conforms.first->lookupDirect(nestedName)) {
       PotentialArchetype *pa;
 
       if (auto assocType = dyn_cast<AssociatedTypeDecl>(member)) {