Re-brand steam-runtime-system-info to be more like a standalone tool

• Belatedly mark v0.20190802.0 as having been released

• Update changelog

  Setting a new version number here will enable us to do a graceful upgrade when files move between packages in the next commit.

• system-info: Move from examples/ to bin/ and install in its own package

  This has become less an example and more a command-line driver for the library, so rename it accordingly.

• system-info: Make the command-line driver relocatable

  Look for shared libraries nearby: go up one level from ${bindir} to ${prefix}, then descend into ${libdir}. This will make it easier to run in a possibly-broken environment, which seems valuable, since its purpose is to detect broken environments.

  (This one breaks CI because dpkg-shlibdeps fails in a merged-/usr container. We might need to backport some dpkg fixes from Debian 10. I'll come back to this later - it isn't essential.)

• system=info: Use a fresh linked list of libraries for each architecture

  Otherwise, if we process an architecture we can run before an architecture we can't, we'll try to free the old list twice. This happens on i386 autobuilders that can't run x86_64 executables.

• system-info: Remove unused variable