Update RNFetchBlobBody.java

Removed duplicated code at line 107

src/android/src/main/java/com/RNFetchBlob/RNFetchBlobBody.java

@@ -103,11 +103,6 @@ public class RNFetchBlobBody extends RequestBody{
         return mime;
     }
     
-    @Override
-    public long contentLength() {
-        return contentLength;
-    }
-    
     @Override
     public void writeTo(BufferedSink sink) {
         try {