Remove one invocation of the ARC optimizer.

Removing one of the invocation of the ARC optimizer. I did not measure any
regressions on the performance test suite (using -O), but I did see a
reduction in compile time on rdar://24350646.

Author: nadavrot

lib/SILOptimizer/PassManager/Passes.cpp

@@ -200,7 +200,6 @@ void AddSSAPasses(SILPassManager &PM, OptimizationLevelKind OpLevel) {
   PM.addDeadStoreElimination();
   PM.addCSE();
   PM.addEarlyCodeMotion();
-  PM.addARCSequenceOpts();
 
   PM.addSILLinker();