f2ser: avoid serialization directives when not needed

[ChristopherBignamini]

According to the current version of f2ser we only want serialization directives of the init/run/finalize subroutine of a given source file. However, pp_ser.py, which is executed on the file generated by f2ser, adds serialization flag check blocks of the type

#ifdef SERIALIZE                  
  REAL(KIND=wp) :: &              
#else                             
  REAL(KIND=wp), INTENT(IN) :: &  
#endif                            

also to other function where we do not add any pre-serialization directive. Assuming we can't change pp_ser.py, is there anything we can do in f2ser to avoid this issue?