Improve implementation of ParserATNSimulator::getConflictingAlts()

PredictionModeClass::getAlts(configs)
yields the same result as
PredictionModeClass::getAlts(
  PredictionModeClass::getConflictingAltSubsets(configs)
)
Both return a BitSet with bits set for all alts which occur in configs.

Signed-off-by: Andreas Buhr <andreas@andreasbuhr.de>

runtime/Cpp/runtime/src/atn/ParserATNSimulator.cpp

@@ -1201,8 +1201,7 @@ Ref<ATNConfig> ParserATNSimulator::ruleTransition(Ref<ATNConfig> const& config,
 }
 
 BitSet ParserATNSimulator::getConflictingAlts(ATNConfigSet *configs) {
-  std::vector<BitSet> altsets = PredictionModeClass::getConflictingAltSubsets(configs);
-  return PredictionModeClass::getAlts(altsets);
+  return PredictionModeClass::getAlts(configs);
 }
 
 BitSet ParserATNSimulator::getConflictingAltsOrUniqueAlt(ATNConfigSet *configs) {