Remove redundant SP only versions of DIST_GRID and GATH_GRID

[samhatfield]

Resolves #126.

Please wait for my signal before merging this -> this depends on a PR to ifs-source to remove calls to _32 subroutines which is under review.

[samhatfield]

I'd like to get this PR merged. As far as I'm aware, the only place these routines were used was in the IFS prototype (and defunct for almost a decade) EnKF. I recently filed a pull request to remove these cases and now there is no instances of GATH_GRID_32 nor DIST_GRID_32 in ifs-source. CY49R1 still has them but CY50R1 will not. The former (and previous) cycles don't use an external ecTrans repository anyway, right?

@RyadElKhatibMF can you confirm that MétéoFrance does not make any use of GATH_GRID_32 nor DIST_GRID_32?

@wdeconinck would you favour completely deleting these routines like in this PR, or leaving in the toplevel subroutines with an abort statement?

[RyadElKhatibMF]

I confirm I can't see any use of GATH_GRID_32 nor DIST_GRID_32

[wdeconinck]

I think in first instance an abort, and then that gives some time for some configurations like DestinE not relying on CY50R1, but definitely happy to use recent ectrans GPU developments to catch up without linking errors.

[samhatfield]

I think in first instance an abort, and then that gives some time for some configurations like DestinE not relying on CY50R1, but definitely happy to use recent ectrans GPU developments to catch up without linking errors.

Sorry, not sure what you mean by that last part?

[wdeconinck]

Sorry @samhatfield I missed your last question before. What I meant is to keep the routines for now but completely empty, except for an abort statement with deprecation message; essentially a dummy. This is just to allow current and older IFS cycles to keep linking with ectrans, even if these routines don't get executed at runtime.
At the same same time of creating this PR, you need to create a PR in ifs-source that removes any notion of this symbol if they are still used at least. If it is true that current IFS cycle does not use this symbol that's great, but it would be good to record somewhere which cycle still expects this symbol.
Then at a subsequent ectrans release which is to be agreed with users of possibly affected cycles, we can fully remove these routines.