Directly do the work that was in the deprecated method.

PiperOrigin-RevId: 648418934

objectivec/GPBMessage.m

@@ -3541,10 +3541,13 @@ GPB_INLINE BOOL GPBIsCaseOfSelForOneOf(const char *selName, size_t selNameLength
   if (self) {
     NSData *data = [aDecoder decodeObjectOfClass:[NSData class] forKey:kGPBDataCoderKey];
     if (data.length) {
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wdeprecated-declarations"
-      [self mergeFromData:data extensionRegistry:nil];
-#pragma clang diagnostic pop
+      GPBCodedInputStream *input = [[GPBCodedInputStream alloc] initWithData:data];
+      @try {
+        [self mergeFromCodedInputStream:input extensionRegistry:nil];
+        [input checkLastTagWas:0];
+      } @finally {
+        [input release];
+      }
     }
   }
   return self;