Workbench: Remove transmission-cli.

The whole transmission source package has been removed in Debian.
Hopefully I'll revert this soon.

workbench/Dockerfile

@@ -141,7 +141,6 @@ RUN apt-get update && \
         tk-dev \
         tmux \
         tnftp \
-        transmission-cli \
         ttyrec \
         udftools \
         unzip \