Remove note about missing ios/tvos targets in platform docs.

I misunderstood how this works, and I have fixed the linux builds
to support ios/tvos.

src/tools/tier-check/src/main.rs

@@ -25,8 +25,6 @@ fn main() {
     let doc_targets: HashSet<_> = doc_targets_md
         .lines()
         .filter(|line| line.starts_with('`') && line.contains('|'))
-        // These platforms only exist on macos.
-        .filter(|line| !line.contains("[^apple]") || cfg!(target_os = "macos"))
         .map(|line| line.split('`').skip(1).next().expect("expected target code span"))
         .collect();