Removed special prefix that was being added when naming RNTuples in APR

Removed special prefix that was being added to create RNTuple names

At the start RNTuple used the same names as corresponging TTrees,
with RNT: prefix added to not confuse the 2. Now this prefix is
removed. Also, RNTuples will now use different names as defined in
POOLCore/APRDefaults - except CollectionTree, which is mentioned in
115 places in the code. Maybe something to address later.
Athena is now also able to read EventTags in RNTuple format (the previous
implementation was not really doing it)