Only build snowflake in alphas or nightlies for mobile
rbm.conf we have
snowflake: '[% c("var/alpha") || c("var/nightly") %]' for mobile. However, we unconditionally compile
and bundle it in
tor-onion-proxy-library. We should bind that to the
rbm.conf, too, though. This would make the release .apks
smaller and would save (re-)build time.