You can uninstall or removes an installed boinc-client package itself from Ubuntu 16.10 (Yakkety Yak) through the terminal,
$ sudo apt-get remove boinc-client
If you would like to remove boinc-client and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove boinc-client
If you use with purge options to boinc-client package all the configuration and dependent packages will be removed.
$ sudo apt-get purge boinc-client
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 boinc-client