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

[via llvm-commits]

enh-google wrote:

(github n00b asks: i see you updated the first comment on the conversation tab in a way that addresses @nikic's question, but do you need to do the _commit message_ on the patch too? i think the answer is no, because github replaces that commit message at "squash and merge" time? otherwise lgtm.)

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