How to uninstall pinentry-gtk from Ubuntu
To uninstall just pinentry-gtk package itself from Ubuntu execute on terminal:
sudo apt-get remove pinentry-gtk
Uninstall pinentry-gtk and it's dependent packages
To uninstall the pinentry-gtk package and any other dependant package which are no longer needed on Ubuntu.
sudo apt-get autoremove pinentry-gtk
If you also want to delete configuration and/or data files of pinentry-gtk from Ubuntu then this will work:
sudo apt-get purge pinentry-gtk
To delete configuration and/or data files of pinentry-gtk and it's dependencies from Ubuntu then execute:
sudo apt-get autoremove --purge pinentry-gtk
pinentry-gtk package information
GTK+-based PIN or pass-phrase entry dialog for GnuPG
This package contains a program that allows for secure entry of PINs or pass phrases. That means it tries to take care that the entered information is not swapped to disk or temporarily stored anywhere. This functionality is particularly useful for entering pass phrases when using encryption software such as GnuPG or e-mail clients using the same. It uses an open protocol and is therefore not tied to particular software. The program contained in this package implements a PIN entry dialog using the GTK+ tool kit version 1. If the X Window System is not active then an alternative text-mode dialog will be used. There are sibling packages that implement PIN entry dialogs using other tool kits.
More information about apt-get remove
Advanced Package Tool, or APT, is a free software user interface that works with core libraries to handle the installation and removal of software on Debian, Ubuntu and other Linux distributions. APT simplifies the process of managing software on Unix-like computer systems by automating the retrieval, configuration and installation of software packages, either from precompiled files or by compiling source code.
apt-get is the command-line tool for handling packages, and may be considered the user's "back-end" to other tools using the APT library.
apt-get remove is identical to install except that packages are removed instead of installed. Note that removing a package leaves its configuration files on the system. If a plus sign is appended to the package name (with no intervening space), the identified package will be installed instead of removed.