libreoffice: replace `openjdk` runtime-input with minimal JRE

Previously, `pkgs.libreoffice` had a total closure-size of 2.4GB where
`pkgs.openjdk` was a significant part:

    $ nix path-info ./result -Sh
    /nix/store/7xyfklmiz2azcnrfa8n9cz12dyyqc85r-libreoffice-7.1.7.2	   2.4G
    $ nix path-info ./result -shr | grep openjdk
    /nix/store/qcn7ihaak9g8ayyj4995ila2z0pkm37i-openjdk-17.0.1+12             	 643.6M

However we need exactly two components:

* a `javac` from `pkgs.openjdk`
* a minimal runtime (i.e. a JRE) for `libofficebean.so` where
  `libjawt.so` is also available.

I moved `jdk` to the `nativeBuildInputs` to ensure that `javac` is still
available in the build-environment and created a minimal JRE that seems
sufficient.

Now, the total closure-size is reduced by ~29.1% (basically the 600M
from `pkgs.openjdk`):

    $ nix path-info ./result -Sh
    /nix/store/zv34xijv64k7sz7rv50g3v6y59qg7p8k-libreoffice-7.1.7.2	   1.7G

0 files changed, 0 insertions, 0 deletions