remove flatpak

Flatpak support has been a HUGE pain to keep working, the builds take
forever and cost me real money, and there are very few users. Ideally,
we want to just use native system packagers for each distro. I thought
Flatpak would make it easy to support many distros but that ended up
being false.

dist/linux/app-flatpak.desktop

@@ -1,14 +0,0 @@
-[Desktop Entry]
-Name=Ghostty
-Type=Application
-Comment=A terminal emulator
-Exec=/app/bin/ghostty
-Icon=com.mitchellh.ghostty
-Keywords=terminal;tty;pty;
-StartupNotify=true
-Terminal=false
-Actions=new-window
-
-[Desktop Action new-window]
-Actions=new-window
-Exec=/app/bin/ghostty