Cleanup unused files from the CTA project

Problem

The CTA project contains some files that are not used anywhere in the project (do not belong to any project target).

This is an example, but there may be others:

• https://gitlab.cern.ch/cta/CTA/-/blob/main/common/log/log.cpp

Proposal

We should find all these files and remove them (unless there is any valid reason to keep them).

In particular, we should check if there are any old castor-era files that are not needed anymore.