suggest to fix license statement

[7c00]

The license statements at the header of many source code look like:

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. ... The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); ...

It seems to be borrowed from some project of ASF. While Palo is not (at least currently) donated to ASF, so it might be not proper to put such statements.

[imay]

Thanks for advise, we will fix it soon.