dashboard: skip Android build on older releases
dashboard: skip Android build on older releases

Also do some cleanup of no longer applicable policy.

Fixes golang/go#30485

Change-Id: Id921ea5e7f60dda097be9ebba052a09349ea000a
Reviewed-on: https://go-review.googlesource.com/c/164681
Reviewed-by: Elias Naur <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@eliasnaur.com>

golang/build,golang/build,golang/build,golang/build