Fix oskar build
Check-out OSKAR at one commit before 3073412c8a332fc34469fd3460e792b21d7cef2e (2020/09/21)
* commit 3073412c8a332fc34469fd3460e792b21d7cef2e (HEAD -> master, origin/master, origin/HEAD)
| Date: Mon Sep 21 23:47:42 2020 +0100
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| Add functions to read data from HDF5 files.
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as this breaks the OSKAR build on CI.