Set pytorch to run on single thread only on docker jobs

To fix the jobs on the docker runners for the CI, I added this line a while back.

We should:

• remove this line as this limits any work to a single thread and is not really wanted for performance reasons.
• add OMP_NUM_THREADS=1 as a variable in the CI config, either on the .gitlab-ci.yaml (in bob/dev-profile) (if possible, only for the jobs running on docker) or in the runner configuration (if possible?).