Remove @brief annotations from Rust API docs (#20769)

programs/bpf/rust/iter/src/lib.rs

@@ -1,4 +1,4 @@
-//! @brief Example Rust-based BPF program tests loop iteration
+//! Example Rust-based BPF program tests loop iteration
 
 extern crate solana_program;
 use solana_program::{custom_panic_default, entrypoint::SUCCESS, msg};