Prune commentary and stale Rust port notes

src/platform.rs

@@ -1,22 +1,3 @@
-//! Capabilities a widget tree needs from whatever is hosting it, that
-//! neither iris nor the app can perform itself.
-//!
-//! Same shape as [`crate::attr::FocusHost`], and for the same reason: the
-//! interface is declared here, below, and implemented by each backend
-//! above (`default/platform.rs`, `android/platform.rs`), so a widget can
-//! ask for the capability by trait bound instead of a caller threading a
-//! callback down through every builder.
-
-/// Hand a URL to whatever the platform opens URLs with.
-///
-/// One method rather than a general "run an intent"/"exec" surface: the
-/// only thing a transcript needs is to follow a link a reader tapped, and
-/// a narrower capability is a narrower thing to get wrong.
-///
-/// **Nothing is reported back.** There is no answer worth branching on --
-/// the platform either shows a browser or does not, and both are outside
-/// this process -- so failures are logged where they happen (each impl)
-/// rather than turned into a `Result` every call site would discard.
 pub trait OpenUrl {
     fn open_url(&mut self, url: &str);
 }