To uninstall xfce4-panel-dev just follow these instructions.
sudo apt-get remove xfce4-panel-dev
This will remove just the xfce4-panel-dev package itself.
sudo apt-get remove --auto-remove xfce4-panel-dev
This will remove the xfce4-panel-dev package and any other dependant packages which are no longer needed.
If you also want to delete your local/config files for xfce4-panel-dev then this will work.
sudo apt-get purge xfce4-panel-dev
Or similarly, like this xfce4-panel-dev
sudo apt-get purge --auto-remove xfce4-panel-dev
|Maintainer||Debian Xfce Maintainers <email@example.com>|
|Home page||http://www.xfce.org/ suite::xfce, uitoolkit::gtk|
|Description||Xfce4 panel development files Xfce4 panel, the main panel of Xfce4 desktop environment. The files in this package are mainly going to be of interest for you if you intend to code applications which use some of the Xfce4 C panel functions.|