Remove unnecessary long/StatusCode conversions

In preparation for a larger re-design of StatusCode clean up a few places where the code unnecessarily relies on an implicit long type-conversion. In detail:

• ObjectVector::remove: Return the index of the deleted object as documented in the base class. Before it always returned 1
• RegistryEntry: Change return type of some methods from long to StatusCode
• IODataManager: Get rid of the S_OK/S_ERROR enum alias as this relies on the actual type of the StatusCode enums
• RootDataConnection: Change return type of setCompression from long to StatusCode
• Replace a few bool-casts with isSuccess() and long-casts with getCode()

GaudiAlg/GaudiAlg/TupleObj.h

@@ -793,7 +793,7 @@ namespace Tuples
     {
       auto scs = std::initializer_list<StatusCode>{
           this->column( std::get<I>( tup ).first, Gaudi::invoke( std::get<I>( tup ).second, value ) )...};
-      auto is_ok = []( const StatusCode& sc ) -> bool { return sc; };
+      auto is_ok = []( const StatusCode& sc ) -> bool { return sc.isSuccess(); };
       auto i     = std::find_if_not( begin( scs ), end( scs ), is_ok );
       if ( i != end( scs ) ) {
         // avoid unchecked StatusCodes...