Change CamusAvroWrapper's signature back to public static

@HenryCaiHaiying Sorry for the careless, I've searched the usage of CamusAvroWrapper and just found one in KafkaAvroMessageDecoder, so I just changed the signature of CamusAvroWrapper recklessly.

PS. Will you guys provide code formating configurations(for intellij or eclipse)? Just found camus match none of my existed ones :)
Sure, i'll shut this PR down and start a new one.