f2ser: remove confusing log messages

[ChristopherBignamini]

In case of array data, we currently check the variable size to decide if add pre-serialization directives to the code as in the following example:

    PRINT *, 'Serializing dz=dz(:,:)'                                 
                                                                      
    IF (SIZE(dz) > 0) THEN                                            
       !$ser data dz=dz(:,:)                                          
    ELSE                                                              
       PRINT *, 'Warning: Array dz has size 0. Not serializing array.'
    END IF                                                            

After running pp_ser.py we get the following code:

    PRINT *, 'Serializing dz=dz(:,:)'                                                        
                                                                                             
    IF (SIZE(dz) > 0) THEN                                                                   
#ifdef SERIALIZE                                                                             
! file: mo_aes_graupel_new.f90_f2ser lineno: #202                                            
SELECT CASE ( ppser_get_mode() )                                                             
  CASE(0)                                                                                    
    call fs_write_field(ppser_serializer, ppser_savepoint, 'dz', dz(:,:))                    
  CASE(1)                                                                                    
    call fs_read_field(ppser_serializer_ref, ppser_savepoint, 'dz', dz(:,:))                 
  CASE(2)                                                                                    
    call fs_read_field(ppser_serializer_ref, ppser_savepoint, 'dz', dz(:,:), ppser_zrperturb)
END SELECT                                                                                   
#endif                                                                                       
    ELSE                                                                                     
       PRINT *, 'Warning: Array dz has size 0. Not serializing array.'                       
    END IF                                                                                   

When SERIALIZE is not defined, we get the confusing log message 'Warning: Array dz has size 0. Not serializing array.'

Moreover, the

PRINT *, 'Serializing dz=dz(:,:)'"

message should be included in #ifdef SERIALIZE code blocks