Refresh our custom squashfs-tools on top of 4.5+
We currently use squashfs-tools 1:4.4-1+0.tails1, whose only differences with 1:4.4-1 are:
- New xattr_initialize_header.patch: avoid randomness in the filesystem caused by uninitialized ‘unused’ field → was just applied upstream (https://github.com/plougher/squashfs-tools/commit/c570c6188811088b12ffdd9665487a2960c997a0), should be part of the next upstream release
- Rebuild for stretch-backports → soon we should be able to rebuild for Buster instead (once all RMs run Buster or newer)
So once the fix is in sid, we could update our custom package to be a mere backport rebuild, with no code changes.