Migrator: Remove Swift 3 @objc migration

Author: slavapestov

lib/Migrator/Migrator.cpp

@@ -132,23 +132,6 @@ Migrator::performAFixItMigration(version::Version SwiftLanguageVersion) {
     LLVMArgs.erase(aarch64_use_tbi);
   }
 
-  if (StartInvocation.getLangOptions().EffectiveLanguageVersion.isVersion3()) {
-    // SE-0160: When migrating, always use the Swift 3 @objc inference rules,
-    // which drives warnings with the "@objc" Fix-Its.
-    Invocation.getLangOptions().EnableSwift3ObjCInference = true;
-
-    // The default behavior of the migrator, referred to as "minimal" migration
-    // in SE-0160, only adds @objc Fix-Its to those cases where the Objective-C
-    // entry point is explicitly used somewhere in the source code. The user
-    // may also select a workflow that adds @objc for every declaration that
-    // would infer @objc under the Swift 3 rules but would no longer infer
-    // @objc in Swift 4.
-    Invocation.getLangOptions().WarnSwift3ObjCInference =
-      getMigratorOptions().KeepObjcVisibility
-        ? Swift3ObjCInferenceWarnings::Complete
-        : Swift3ObjCInferenceWarnings::Minimal;
-  }
-
   const auto &OrigFrontendOpts = StartInvocation.getFrontendOptions();
 
   assert(OrigFrontendOpts.InputsAndOutputs.hasPrimaryInputs() &&