Clean up APIs before declaring API 28.

As part of finalizing an SDK, we need to ensure that no new APIs are
marked @Deprecated, since they're typically cleanup that someone
forgot to finish.

Someone forgot to replace Slice.getTimestamp() with Slice.getLong().

Bug: 77588754
Test: builds, boots
Exempt-From-Owner-Approval: SDK finalization
Change-Id: Ic0ec91a43d161a69c1e840c42046ad500b7aeca0