preInclude.SleptonsLLP.py: Drop use of ExtraParticles.PDGHelpers module - not required for digitization
As this branch is not intended to be used for simulation (only digitization onwards). Then it is safe
to drop the usage of the
ExtraParticles.PDGHelpers module, which is intended to manage files being
updated at multiple points during the configuration of the the simulation step - this functionality
is not required for later steps. This should fix the issues seen in ATLMCPROD-10493 (ADCSUPPORT-5537).