Remove unused dead code.

Nothing refers to this code.

PiperOrigin-RevId: 622175593

src/google/protobuf/compiler/objectivec/extension.cc

@@ -134,14 +134,6 @@ void ExtensionGenerator::DetermineNeededFiles(
   }
 }
 
-void ExtensionGenerator::GenerateRegistrationSource(
-    io::Printer* printer) const {
-  printer->Emit({{"full_method_name", full_method_name_}},
-                R"objc(
-                  [registry addExtension:$full_method_name$];
-                )objc");
-}
-
 }  // namespace objectivec
 }  // namespace compiler
 }  // namespace protobuf

src/google/protobuf/compiler/objectivec/extension.h

@@ -34,7 +34,6 @@ class ExtensionGenerator {
 
   void GenerateMembersHeader(io::Printer* printer) const;
   void GenerateStaticVariablesInitialization(io::Printer* printer) const;
-  void GenerateRegistrationSource(io::Printer* printer) const;
   void DetermineObjectiveCClassDefinitions(
       absl::btree_set<std::string>* fwd_decls) const;
   void DetermineNeededFiles(