SIL: remove the pinning instructions: strong_pin, strong_unpin, is_unique_or_pinned

They are not used anymore after removing the pinning addressors.

lib/SILOptimizer/Transforms/ArrayElementValuePropagation.cpp

@@ -191,7 +191,6 @@ bool ArrayAllocation::recursivelyCollectUses(ValueBase *Def) {
     auto *User = Opd->getUser();
     // Ignore reference counting and debug instructions.
     if (isa<RefCountingInst>(User) ||
-        isa<StrongPinInst>(User) ||
         isa<DebugValueInst>(User))
       continue;