This makes it easy to retrieve the project version at runtime
for display purposes, while simplifying the export preset configuration.
You can now leave the version empty unless you need to override it on a per-preset
basis.
Since export presets save the values of default values to the `export_presets.cfg`
file, this change only affects export presets created after this commit was merged.
We don't use that info for anything, and it generates unnecessary diffs
every time we bump the minor version (and CI failures if we forget to
sync some files from opt-in modules (mono, text_server_fb).
