Revert "apt install ocp-indent instead of via opam"
Revert "apt install ocp-indent instead of via opam"

This reverts commit df2d401a6838b710517c07c6e8ea771ea7129b01.

https://github.com/goblint/analyzer/pull/308#issuecomment-889724301:

In the run https://github.com/goblint/analyzer/runs/3199968802, we have the error message

```
ocp-indent file: src/analyses/arinc.ml, lines: 122
ocp-indent: internal error, uncaught exception:
            Failure("Config file not found - neither /etc/ocamlfind.conf nor the directory /etc/ocamlfind.conf.d")
```

goblint/analyzer,goblint/analyzer,goblint/analyzer,goblint/analyzer,goblint/analyzer