ping**(5./7.) [patch, fortran] Fix memory leak on deallocation

[Thomas König]

> In the meantime, here is a patch which fixes a regression I introduced
> when fixing a regression with a memory leak.  The important thing
> here is to realize that we do not need to finalize (and deallocate)
> multiple times for the same expression and the same component
> in the same namespace.  It might cause code size regressions, but
> better big code than wrong code...
> 
> This is a regression all the way down to gcc 8.  OK for all affected
> branches?

Ping?

Unless there are any objections, I would commit this to master
on Sunday.

Regards

	Thomas