Minor, delete unused method in DataFlowInfo
Minor, remove duplicate method in ExpressionCodegen
Minor, fix some warnings in codegen
Fix initialization of object's INSTANCE$ field

Call object's constructor in <clinit> and ignore the result, but in the first
line of <init> save the current "this" to INSTANCE$

 #KT-4516 Fixed
 #KT-4543 Fixed
 #KT-5291 Fixed
 #KT-5523 Fixed
 #KT-5582 Fixed
Move properties of enum class object to the enum class

Similar to how it's done for usual classes