The self-updater is now a requirement for the main app to be able to be
built. You no longer need the existing binary. This makes it easier for
anyone to just try out the app locally and makes reproducible builds
also possible.
(This is done because the self-updater code will soon be moved to a
separate package, and I want to make this entire updater process
as simple as possible.)
In order to avoid the self-updater app from appearing as a product when
archiving a build, SKIP_INSTALL is set to true. This avoids a variety
of annoying issues including the archive appearing under "Other Items".
