libbrotli has updated its .pc files since the last sed was written, so
it didn't work anymore, resulting in Toxic build failing. However, the
way they have updated it, it's still broken, so a different sed is
needed.
The Docker detection method doesn't work on cgroup v2 systems, so the
script just keeps erroring out.
There doesn't seem to be a simple way to detect that we are running
inside a Docker container, so it makes sense to drop that check
altogether.
The intention is that JFreegman would run it locally on his machine for
every Toxic release and publish the build artifacts on GitHub for
download, similarly to how the qTox team makes release builds. This
should mitigate the loss of the Jenkins build server to some extent,
which used to provide Toxic builds before.
