Revert "Master is now S"

This reverts commit 566b114bde4a96d6f5dbbab69d4982c78867f623.

Reason for revert: BuildCompat.isAtLeastR is broken: b/154661881

Change-Id: I45ab84f681bd6dc9a0ce6f40eb8792b0102f2c42
(cherry picked from commit ca41780bf04dc4aab43c91aa9e6a85d886e9bf3c)
21 files changed