The acceptance tests have not been testing the extension itself,
have not been maintained for quite some time, and do not serve
as a good example anymore.
Until we have a proper set of example acceptance tests, we should
remove them.
Also drop the now-unused dependency on Codeception.
- configure the checked paths via the configuration file
- do not output a progress bar on CI
- add a baseline file and a command for creating it
- cap the number of processes
Fixes#281