Transmission is a meta-package, if you uninstall it, it does not remove the other packages it depends upon.
Description-en: lightweight BitTorrent client
Transmission is a set of lightweight BitTorrent clients (in GUI, CLI
and daemon form). All its incarnations feature a very simple, intuitive
interface on top on an efficient, cross-platform back-end.
This is just a metapackage depending on one of the front-end
Are you running out of space ? Could you install the other client of your choice keeping transmission ? transmission-gtk is part of ubuntu-desktop dependencies.