Remove code to mock Flatpak commands for tests
Remove code to mock Flatpak commands for tests

Sufficiently new Flatpak is available and installed for the full
test matrix, so there is no reason to carry the mock-flatpak code
paths, which need quite a bit of maintenance as flatpak-module-tools
evolves.

Signed-off-by: Owen W. Taylor <ea9e9dc5381b1dcdec5e0e8197a67fa819b36a07@fishsoup.net>

projectatomic/atomic-reactor,DBuildService/atomic-reactor,fr34k8/atomic-reactor,DBuildService/atomic-reactor,projectatomic/atomic-reactor,fr34k8/atomic-reactor