remove deprecated warning in albertagrid backuprestore facilities

Simon Praetoriusrequested to merge
simon.praetorius/dune-grid:issue/alberta_backuprestore_warning into master

Summary

Remove the usage of writeGridXdr and readGridXdr in AlbertaGrid since is produces a deprecated warning.

Details

The functions writeGridXdr and readGridXdr were simplified to writeGrid and readGrid some time ago, but used in the backup-restore facilities of the AlbertaGrid. This emits a deprecated warning all the time. This MR, replaces the old functions with the new ones.

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