This removes the convoluted steps in docker-build.sh in favour of
integrating the web-build sequence into the Debian rules file
explicitly. This will allow the web-build to work properly outside of
the boutique Docker container we build, thus allowing it to be build
properly directly on a target system with dpkg-buildpackage.
Without this, when building the `jellyfin-nightly` package, it attempts
to find service/init files with the name `jellyfin-nightly` instead of
the proper name. This override prevents this by forcing the name to
`jellyfin`. Required for nightly builds.
