Override of DU_avg1 and DV_avg1 when using UV_PSOURCE

[arango]

In ​src:ticket:384 I mentioned that the override of barotropic, time filtering arrays DU_avg1 and DV_avg1 is unnecessary in routine step2d, when the point sources (river runoff) option UV_PSOURCE is activated. In this ticket, I proposed that, if this is actually needed this computation needs to be done at the nfast(ng)+1 when all the barotropic time-filtering is finalized:

      IF ((iif(ng).eq.(nfast(ng)+1)).and.PREDICTOR_2D_STEP(ng)) THEN

#  ifdef UV_PSOURCE
        DO is=1,Nsrc
          i=Isrc(is)
          j=Jsrc(is)
          IF (((IstrR.le.i).and.(i.le.IendR)).and.                      &
     &        ((JstrR.le.j).and.(j.le.JendR))) THEN
            IF (INT(Dsrc(is)).eq.0) THEN
              DU_avg1(i,j)=Qbar(is)
            ELSE
              DV_avg1(i,j)=Qbar(is)
            END IF
          END IF
        END DO
#  endif
        ...
      END IF

I have some time to think and test the need of this code. It turns out that this is totally redundant. The algorithm takes care of this when computing the local transports DUon and DVom. At the point sources locations, the value of DU_avg1 or DV_avg1 is exactly the same as Qbar.

I don't recall how this was introduced in the code. As a matter of fact, the original formulation corrected in ​src:ticket:384 was wrong! This is a good example of how the adjoint model help us (in a very hard way to find) to track redundant computations. In this case the redundant computation was wrong.