Add RomanPot and OffMTracker particles.

benchmarks/far_forward/scripts/print_far_forward_protons.cxx

@@ -19,7 +19,6 @@ using namespace ROOT::VecOps;
 
 int print_far_forward_protons(const char* fname = "topside/rec_far_forward_protons.root")
 {
-  ROOT::EnableImplicitMT();
   ROOT::RDataFrame df("events", fname);
 
   auto df0 = df.Range(10);