Draft: Improve cellmode exporter

The original cell mode exporter checks the metadata file for the cells variable. This is no longer a useful check as the deployment playbook does not do anything with that variable.

Instead, we replace it by a check on the systemd service that looks for the -l argument that is passed to iocsh which provides a more robust way to detect the use of cell mode in an IOC.

Note that there is a further change in this to remove start_ioc.sh from the deployment directory and instead to merge it into the actual startup script. This was originally necessary to try to simplify the fetching of systemd data, but it seems to me to be useful as a simplification nonetheless.

Furthermore, note that this change stops all use of iocsh.bash in all IOCs; previously we had dropped it from the NFS e3 IOCs, but this also strips it from the conda ones as well.