[llvm] [Android] Drop workarounds for older Android API levels pre 9, 17 and 21 (PR #161911)

[via llvm-commits]

enh-google wrote:

and, no, sadly we don't have Android documentation [that i know of --- @DanAlbert ?] that tells you either (a) what our policy is or (b) what that policy means in practice at any given time.

there's extensive documentation of (a) _internally_, and you can _infer_ (b) from the lowest `__INTRODUCED_IN()` in the headers in the ndk ... but there's no public doc i can think of. to be fair, it's quite complicated; it's not time-based, and it's not _just_ usage-based because obviously some things are much more painful to support than others.

https://github.com/llvm/llvm-project/pull/161911