You can uninstall or removes an installed aspell-bn package itself from Ubuntu 16.04 LTS (Xenial Xerus) through the terminal,
$ sudo apt-get remove aspell-bn
If you would like to remove aspell-bn and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove aspell-bn
If you use with purge options to aspell-bn package all the configuration and dependent packages will be removed.
$ sudo apt-get purge aspell-bn
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 aspell-bn