You can uninstall or removes an installed libcusolver7.5 package itself from Ubuntu 16.04 LTS (Xenial Xerus) through the terminal,
$ sudo apt-get remove libcusolver7.5
If you would like to remove libcusolver7.5 and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove libcusolver7.5
If you use with purge options to libcusolver7.5 package all the configuration and dependent packages will be removed.
$ sudo apt-get purge libcusolver7.5
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 libcusolver7.5