flatpak: Hitori now only builds with Meson

The Autotools support was recently removed, but the Flatpak manifest
hadn't been updated.

This commit fixes this omission.
1 job for bochecha/flatpak/meson in 17 minutes and 51 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #226016
build-and-test

00:17:51