Remove unused variable

Change-Id: I2ca87b9e944ce9613f63cee7af81f5556a67b5e8

Author: wesm

java/vector/src/main/java/org/apache/arrow/vector/stream/MessageSerializer.java

@@ -169,8 +169,6 @@ public static ArrowRecordBatch deserializeRecordBatch(ReadChannel in,
    */
   public static ArrowRecordBatch deserializeRecordBatch(ReadChannel in, ArrowBlock block,
       BufferAllocator alloc) throws IOException {
-    long readPosition = in.getCurrentPositiion();
-
     // Metadata length contains integer prefix plus byte padding
     long totalLen = block.getMetadataLength() + block.getBodyLength();