Revert "third_party/protobuf: Update to HEAD (83d681ee2c)"

third_party/protobuf/objectivec/GPBWireFormat.m

Index: third_party/protobuf/objectivec/GPBWireFormat.m
diff --git a/third_party/protobuf/objectivec/GPBWireFormat.m b/third_party/protobuf/objectivec/GPBWireFormat.m
index 860a339f9a2c9c9e31dc53fad97011d83c682213..193235d6ce41e502e293eb36e4c6e85f0c36360d 100644
--- a/third_party/protobuf/objectivec/GPBWireFormat.m
+++ b/third_party/protobuf/objectivec/GPBWireFormat.m
@@ -49,13 +49,6 @@ uint32_t GPBWireFormatGetTagFieldNumber(uint32_t tag) {
   return GPBLogicalRightShift32(tag, GPBWireFormatTagTypeBits);
 }
 
-BOOL GPBWireFormatIsValidTag(uint32_t tag) {
-  uint32_t formatBits = (tag & GPBWireFormatTagTypeMask);
-  // The valid GPBWireFormat* values are 0-5, anything else is not a valid tag.
-  BOOL result = (formatBits <= 5);
-  return result;
-}
-
 GPBWireFormat GPBWireFormatForType(GPBDataType type, BOOL isPacked) {
   if (isPacked) {
     return GPBWireFormatLengthDelimited;