Remove comment which is no longer correct, z_mergetoaddress has locked notes for a long time now

src/wallet/asyncrpcoperation_mergetoaddress.cpp

@@ -182,7 +182,6 @@ void AsyncRPCOperation_mergetoaddress::main()
 
 // Notes:
 // 1. #1359 Currently there is no limit set on the number of inputs+outputs, so size of tx could be invalid.
-// 2. #1277 Spendable notes are not locked, so an operation running in parallel could also try to use them.
 bool AsyncRPCOperation_mergetoaddress::main_impl()
 {
     assert(isToTaddr_ != isToZaddr_);