HLAPI Android: Remove Guava dependencies

[afandria]

ImmutableList, ImmutableMap, and SettableFuture are the most likely things that we should remove if possible. The goal is to reduce final binary size and because use of Guava is discouraged on Android.

Note: It might be impossible to complete this because we are built on the low-level Java API (for vom, at least), so part of this issue is to investigate whether it's even possible to do so.