Sema: Remove validateAbstractStorageDecl()

Validating a variable or subscript no longer forces accessor synthesis.

lib/Sema/CodeSynthesis.cpp

@@ -1404,6 +1404,10 @@ void TypeChecker::synthesizeWitnessAccessorsForStorage(
                                              AbstractStorageDecl *storage) {
   bool addedAccessor = false;
 
+  // Make sure the protocol requirement itself has the right accessors.
+  // FIXME: This should be a request kicked off by SILGen.
+  DeclsToFinalize.insert(requirement);
+
   requirement->visitExpectedOpaqueAccessors([&](AccessorKind kind) {
     // If the accessor already exists, we have nothing to do.
     if (storage->getAccessor(kind))