build: Remove leftover flatpak patch
The flatpak version used was changed in 406db6c5
This patch had been merged into flatpak upstream by 1.5.1 b121b288253b9b621e5305d228191e6751e64c88
The flatpak version used was changed in 406db6c5
This patch had been merged into flatpak upstream by 1.5.1 b121b288253b9b621e5305d228191e6751e64c88