Now that the stable release is on the same codebase, it should be less
necessary to have 2 development builds.
Also since most performance issues have been fixed, it should not be
necessary anymore to build the nightly version in release mode.
This drops the script we used to build fractal. And uses know only
meson. This also drops the need for specifying sources since cargo does
that for us.
This also bumps the meson version.
This also drops the build option `skip-cargo-build`.
Most of the changes are comming from https://gitlab.gnome.org/World/pika-backup
