This reverts commit 82d09560c6.
It doesn't work - the setup scripts are expecting a ".bin" file (which
is apparently a 7z archive), but what's actually got is a ".zip".
Conflicts:
buildserver/provision-android-ndk
`fdroid build` handles setting the NDK env vars since the NDK version can
change depending on the app being build. Unlike ANDROID_HOME, there is no
single global NDK location. The NDK installs are all versioned.