[platforms/hwcomposer] Remove integration with VirtualTerminal

The hwcomposer plugin doesn't need it. It was only created for the
need of libinput relying on it. As libinput doesn't need it any more,
hwcomposer doesn't need to integrate with VirtualTerminal.

Reviewers: Plasma

Subscribers: plasma-devel

Projects: Plasma

Differential Revision: https://phabricator.kde.org/D1444