Hack around hack for missing CSC Raw2Digi->Digi2Raw converter

Create separate customize function to redirect inputs so that the mixed digis are used for CSC, not the hard-scatter ones only.  PreMixing will now need to be invoked using 
--customise SLHCUpgradeSimulations/Configuration/postLS1CustomsPreMixing.customisePostLS1
for the post LS1 configuration.