Revert "fix(css): Set page `size: auto` instead of `size: A4`"

[mejo-]

This reverts commit ef54c5244efdc2d62f0c306b1f6ed5195e027552.

Turns out this has undesired effects and we really want to set a default size value different than auto.

🏁 Checklist

• [x] Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• [x] Sign-off message is added to all commits

[mejo-]

/backport to stable30

[mejo-]

/backport to stable29

[backportbot[bot]]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/6668/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 17bad670

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/6668/stable29

Error: No changes found in backport branch

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.