Since we are pre-processing anyway the AppStream metadata file (because
appstream-glib doesn't pass unknown XML attributes, cf. a previous
commit), it does feel silly now to continue loading the file at runtime
too. Let's just pre-process more data into the constructed C files, i.e.
get the introduction paragraphs and the change items too.
The only other remaining advantage of appstream-glib was that it was
handling the localization but since we also have these localized strings
in our gettext files, we can as well translate with gettext as any other
strings and it works just fine.
It will also get rid of any packaging issue, forgetting to package the
metadata file (as we had on the Windows installer, and still have on the
macOS package). Now it will just always work because data is internal.
10d8765101