default-jre and java dependencies dependencies had been added initially
[1] because of libreoffice-java-common, which is no longer present.
Then, when the image was changed from ubuntu to alpine [2], default-jre
was replaced with openjdk-8.
If java is still a dependency for libreoffice, then it should be pulled
automatically.
[1] 9ecdb9e995
[2] 650ae6eee1
PDFtk actually isn't needed. It was being used for breaking a PDF
into pages but this is something that be replaced by the already present
'pdftoppm'. Furthermore, by removing this dependency we contribute to
reproducible builds and overall supply chain security because it was
obtained from gitlab with no signature verification or version pinning.
The replacement 'pdftoppm' enabled us to do a shortcut:
- before: PDF -> PDF pages -> PNG images -> RGB images
- after: PDF -> PPM images -> RGB images
And this last conversion step is trivial since the RGB format we were
using is just a PPM file without the metadata in its header.
