Merge branch 'issue/alberta_backuprestore_warning' into 'master'

ref:core/dune-grid

### 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.

See merge request [!338]

  [!338]: gitlab.dune-project.org/core/dune-grid/merge_requests/338