Replace pylammps with lammps or remove pylammps entirely as pylammps should not be used for production

**Description of the error**
Currently, we use PyLAMMPS in MDMC, which is the main MD engine that is currently used. At some point in the far, far future, MDMC will be open-sourced and used by researchers. However, we need to state that MDMC is for demonstration/testing only when used with the MDMC LAMMPS engine and not used for any serious research, e.g., for publication.

Axel Kohlmeyer states the following

in a forum at https://matsci.org/t/issue-with-accessing-thermo-data-in-pylammps/52298.