refactor: Slim down the build image (part 2) - #41

build/packages-template/bigbluebutton/build.sh writes a control file and
calls equivs-build, so equivs is not unused after all; it pulls debhelper
back in as a dependency. Every other removal stands: a search of all
build.sh scripts, .gitlab-ci.yml and the GitHub workflow for the binaries
of the removed packages finds no other use inside the image.

…present

libapr1-dev used to pull libsctp-dev into the image, and coturn's configure
compiles its SCTP transport whenever /usr/include/netinet/sctp.h exists. Without
the header the turnserver, turnadmin and turnutils binaries of bbb-coturn come
out smaller and without SCTP support, the only difference a full build of all
packages found between this image and the current one. Installing libsctp-dev
explicitly keeps bbb-coturn byte-for-byte equivalent; the proper home for it is
the apt-get line in build/packages-template/bbb-coturn/build.sh.

Two more things a full build of every package turned up:

- coturn's configure runs lsb_release -si and, when it answers "Ubuntu", keeps
  LIBEV_OK off as a workaround for send_data_from_ioa_socket_nbh(). Without
  lsb-release the probe is silent and turnserver and turnadmin get the other
  code path. lsb-release stays.

- Go records GOROOT and GOPATH in every binary it builds (the builds do not
  use -trimpath). The current image extracts Go into / and uses
  GOPATH=/tools/go, so bbb-graphql-middleware, bbb-webrtc-recorder and
  bbb-livekit change when the tools move. The two no-op "mkdir tools" and
  "cd tools" lines are still removed, but sbt and Go keep landing in / and
  GOPATH stays /tools/go. Relocating the tools belongs with the image that
  changes how things are installed.

…launcher

Changes how the remaining tools are installed without changing what is
installed. The image goes from 2.95 GB to 2.17 GB on disk and from 727 MB to
561 MB compressed (the current image is 5.45 GB and 1.46 GB).

- One apt layer with --no-install-recommends, cleaned in the same layer;
  manuals, docs, info pages and locales are excluded through dpkg, copyright
  files stay. The empty man directories stay too: update-alternatives in the
  JDK postinst fails without them.
- openjdk-21-jdk-headless instead of openjdk-21-jdk, which pulled the X11 and
  GTK libraries of the full JDK.
- Node from the official tarball instead of nvm, without the C headers
  (node-gyp fetches them on demand; no package build compiles an addon).
- Go 1.27.3 without test, doc, misc and api, still at /go with
  GOPATH=/tools/go: Go records both paths in every binary it builds.
- sbt as the launcher only; the repository preloaded in the zip (150 MB) is
  dropped, the launcher fetches the pinned sbt into the mounted ivy cache.
- The dev libraries the FreeSWITCH modules in modules.conf need, plus
  systemd-dev (bbb-record-core's build.sh asks pkg-config for the systemd unit
  directory, and the systemd package that used to provide systemd.pc is no
  longer pulled in), libsctp-dev and lsb-release for coturn, uuid-dev for
  libks, equivs for the meta-package, python3-pip for the mediasoup worker.

All 31 packages of v4.0.x-develop plus the bigbluebutton meta-package were
built with this image and with the current one on the same host and compared
deb by deb (control fields, file lists, contents, ELF sets, ldd): identical
apart from version strings, timestamps and the SNAPSHOT jar names.