Remove use of `icontext` in `lfric_xios_action_mod`

### Are there any linked Issues or Pull Requests?

ticket:4313

### Brief description

It is currently necessary to include use `icontext, only: xios_get_current_context` in the `lfric_xios_action_mod` when using XIOS revisions pre Changeset 1673. From r1673 the xios_get_current_context subroutine has been included in the XIOS wrapper module.

We currently use r1537 for the coupled application.

### Further details of the issue.

The use of icontext needs removing from these locations:

https://github.com/MetOffice/lfric_core/blob/4637bb3f67566b47278c8ab04444f28dfeb67272/components/lfric-xios/source/lfric_xios_action_mod.f90#L39

https://github.com/MetOffice/lfric_core/blob/4637bb3f67566b47278c8ab04444f28dfeb67272/components/lfric-xios/build/import.mk#L7

Start with components/lfric-xios/source/lfric_xios_action_mod.f90 and components/lfric-xios/build/import.mk at the referenced locations. Check how the XIOS wrapper provides xios_get_current_context, then remove the icontext use from both files and confirm the lfric-xios component still builds with the configured XIOS revision.

Written by the indexing model from the issue text.