We never ended up using yuzu_tester.
Removing it saves code duplication with yuzu_cmd, and distribution size on
prebuilt packages.

For unit testing, we can use catch2 from guest code and dump the results
to a file. Then execute yuzu from a script on ci if we want this to be
automated.

Completely removes all usages of the global system instance within the
services code by passing in the using system instance to the services.