flutter start no longer depends on a pre-built SkyShell.apk. It builds a
new one, as long as an AndroidManifest.xml exists.
We rebuild the .apk every time either AndroidManifest.xml or
flutter.yaml changes.
Turns out linux does have an ideviceinstaller package
however it doesn't contain idevice_id or any of the
other tools we use. Furthermore we don't have
xcrun or the rest of xcode on linux so we can't
manipulate simulators either.
No sense in printing out a warning that ios isn't supported
every time on linux, so I wrapped that block in osx only.
@chinmaygarde @devoncarew
