meso: reconsider the "no insertion if it causes extra jamming" check

[namdre]

it was originally added to improve the way calibrators work but it's not realistic when vehicle insertions at the network border simply model the flow from upstream (which can surely cause jamming).

The problem seldomly comes up due to the additional condition hasBlockedLeader.
It does become apparent when inserting at a tls and using --meso-tls-penalty since this does not causing blocking.