gitlab-ci: keep transitional code in `fdroid build` job
gitlab-ci: keep transitional code in `fdroid build` job

This transitional block of code for installing fdroid/sdkmanager needs to
remain until the buildserver is upgraded to handle all that.

The `fdroid build` is meant to provide a CI run as close as possible to the
production buildserver.  It should not include custom setup or methods,
except when there is no other way to make this job work.  Android's
sdkmanager is definitely part of the buildserver setup, and is included in
the fdroidserver:buildserver image.

Also, `sdkmanager --licenses` is totally inappropriate for F-Droid, and also
already handled by the buildserver provisioning.  F-Droid only accepts the
licenses that match free software source code.  Google has separate licenses
for libraries that have free source vs proprietary source.  F-Droid will
never accept the licenses that are tied to proprietary source.

Also, the CI env var needs to remain set.  Unsetting it here creates an
custom, undocumented, brittle setup.

This reverts !11367 !11476 and upgrades fdroid/sdkmanager to 0.6.1

f-droid/fdroiddata,f-droid/fdroiddata