This reverts commit 378426fe.

> --2017-09-17 12:12:00--  https://github.com/greenplum-db/gporca/releases/download/v2.45.0/bin_orca_centos5_release.tar.gz
> Resolving github.com... 192.30.255.113, 192.30.255.112
> Connecting to github.com|192.30.255.113|:443... connected.
> HTTP request sent, awaiting response... 404 Not Found
> 2017-09-17 12:12:00 ERROR 404: Not Found.