Reverts third_party/protobuf: Update to HEAD (f52e188fe4)

third_party/protobuf/objectivec/GPBProtocolBuffers.m

Index: third_party/protobuf/objectivec/GPBProtocolBuffers.m
diff --git a/third_party/protobuf/objectivec/GPBProtocolBuffers.m b/third_party/protobuf/objectivec/GPBProtocolBuffers.m
index d04c8be155ff1fd18d387a62e8dd156120630559..8512af7e605ec50f32d356188359c9673276e206 100644
--- a/third_party/protobuf/objectivec/GPBProtocolBuffers.m
+++ b/third_party/protobuf/objectivec/GPBProtocolBuffers.m
@@ -31,14 +31,6 @@
 // If you want to build protocol buffers in your own project without adding the
 // project dependency, you can just add this file.
 
-
-// This warning seems to treat code differently when it is #imported than when
-// it is inline in the file.  GPBDictionary.m compiles cleanly in other targets,
-// but when #imported here it triggers a bunch of warnings that don't make
-// much sense, and don't trigger when compiled directly.  So we shut off the
-// warnings here.
-#pragma clang diagnostic ignored "-Wnullability-completeness"
-
 #import "GPBArray.m"
 #import "GPBCodedInputStream.m"
 #import "GPBCodedOutputStream.m"
@@ -54,13 +46,15 @@
 #import "GPBWellKnownTypes.m"
 #import "GPBWireFormat.m"
 
+// Duration and Timestamp are #imported into GPBWellKnownTypes.m to the
+// Objective C categories added will always be linked in with the classes.
 #import "google/protobuf/Any.pbobjc.m"
 #import "google/protobuf/Api.pbobjc.m"
-#import "google/protobuf/Duration.pbobjc.m"
+// #import "google/protobuf/Duration.pbobjc.m"
 #import "google/protobuf/Empty.pbobjc.m"
 #import "google/protobuf/FieldMask.pbobjc.m"
 #import "google/protobuf/SourceContext.pbobjc.m"
 #import "google/protobuf/Struct.pbobjc.m"
-#import "google/protobuf/Timestamp.pbobjc.m"
+// #import "google/protobuf/Timestamp.pbobjc.m"
 #import "google/protobuf/Type.pbobjc.m"
 #import "google/protobuf/Wrappers.pbobjc.m"