buildserver: support any recent NDK version, with stable filenames
buildserver: support any recent NDK version, with stable filenames

Now that the download file name and type seems to have stabilized, I
think we no longer need to manually specify each new added release in
this script to unpack.

closes #331

f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroid-server,fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroidserver