Remove `getentropy` on iOS/tvOS/watchOS/visionOS?

[madsmtm]

This is marked available everywhere in the sys/random.h header, but the header only exists on the macOS SDK.

I've filed FB23000895 with Apple, let's wait to hear back from them before we remove it from libc.

Split out from #5158.

[tgross35]

Similar to #5410 I'd say mark them deprecated, we can remove them in a few versions if we don't hear back.