Remove all gogoproto extensions

This commit removes the following gogoproto extensions;

- gogoproto.nullable
- gogoproto.customename
- gogoproto.unmarshaller_all
- gogoproto.stringer_all
- gogoproto.sizer_all
- gogoproto.marshaler_all
- gogoproto.goproto_unregonized_all
- gogoproto.goproto_stringer_all
- gogoproto.goproto_getters_all

None of them are supported by Google's toolchain (see #6564).

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

api/events/task.proto

@@ -30,7 +30,7 @@ message TaskCreate {
 	string container_id = 1;
 	string bundle = 2;
 	repeated containerd.types.Mount rootfs = 3;
-	TaskIO io = 4 [(gogoproto.customname) = "IO"];
+	TaskIO io = 4;
 	string checkpoint = 5;
 	uint32 pid = 6;
 }