You can uninstall or removes an installed autoconf2.59 package itself from Ubuntu 16.04 LTS (Xenial Xerus) through the terminal,
$ sudo apt-get remove autoconf2.59
If you would like to remove autoconf2.59 and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove autoconf2.59
If you use with purge options to autoconf2.59 package all the configuration and dependent packages will be removed.
$ sudo apt-get purge autoconf2.59
If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.
$ sudo apt-get purge --auto-remove autoconf2.59