Removed shared labels in do loops

[bendudson]

Fixes warnings from grd/grdcomp like

Fortran 2018 deleted feature: Shared DO termination label 2208 at (1)

[holm10]

This is probably the same error that raises warnings in the other packages as well? E.g. the warnings raised during the automated checks for com/comutil, svr/daspk, svr/nksol, svr/vodpk, svr/daux1, api/fmombal, and api/inelrates. Would it be straightforward to apply the same fix to the other packages too?

[bendudson]

@holm10 Yes I think most of the warnings are related to shared labels on nested DO loops

    do 10 i = 1, n
        do 10 j = 1, m
          blah blah
10

should be replaced by something like

    do i = 1, n
        do j = 1, m
          blah blah
        end do
    end do

I started with grd because it seemed quite straightforward compared to other code. Most fixes should be straightforward, but shared labels can be confusing e.g. issue #44

[holm10]

Thanks, @bendudson. I suggest to fix them all in this PR, I could give it a go myself later this week. We'll have to run #44 by @trognlien, I'd say.

[holm10]

@bendudson I fixed the simple warnings associated with the DO-loops. Plenty of places that don't raise warnings where the labels could be replaced. Compiler still throws a bunch of errors for comutil: mostly some very nasty logical loops using arithmetic IF statements (and deprecated ASSIGN calls). It'd be nice to fix all of these at some point, but I'm ot sure what it would take to assert that the rewrite is logically equivalent...