Remove special field EVENT, add parameter event_variables to FunTuple

See description in Analysis!875 (merged).

Work towards DPA task https://gitlab.cern.ch/lhcb-dpa/project/-/issues/121.

DaVinciExamples/python/DaVinciExamples/tupling/option_davinci_tupling_from_collections.py

@@ -72,8 +72,6 @@ variables = {
     "D0": field_vars,
     "Kminus": field_vars,
     "piplus": field_vars,
-    #special field name "EVENT" (like "ALL")
-    "EVENT": evt_vars,
 }
 
 my_tuple = Funtuple(
@@ -81,6 +79,7 @@ my_tuple = Funtuple(
     tuple_name="DecayTree",
     fields=fields,
     variables=variables,
+    event_variables=evt_vars,
     inputs=d02kpi_data)