Tracking: cmake cleanup

First batch of cmake cleanups for Tracking packages. There is a large amount of changes. Most of them were done programmatically, so it should be OK as long as it compiles. The MR is split into several commits (please do NOT squash) describing the changes that were done. In summary:

• remove atlas_depends_on_subdirs
• do not install component headers
• update external and library dependencies (i.e. remove the Eigen dependency that seems to appear almost everywhere but is not actually used by the code directly)
• enable flake8 where applicable