Remove deprecated features: compatlog, commandpipe

[dnsmichi]

#6031
#6033
#6032

[rippiedoos]

If you remove this feature, could you please remove it properly (or fix it in 2.10). Version 2.10 breaks this feature but it's still working in 2.9.2. It is even in the documentation. If you enable the statusdata-feature in 2.10 the objects.cache-file isn't created anymore.
If you run the command icinga2 object list --type=StatusDataWriter in 2.10 it crashes. In 2.9.2 it returns the proper output.

[dnsmichi]

The above was fixed, on removal it won't influence anything else.