Add libstd support to Rust BPF (#5788)

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

@@ -1,15 +1,8 @@
 //! @brief Example Rust-based BPF program that moves a lamport from one account to another
 
-#![no_std]
-#![allow(unreachable_code)]
-#![allow(unused_attributes)]
-
-#[cfg(not(test))]
-extern crate solana_sdk_bpf_no_std;
 extern crate solana_sdk_bpf_utils;
-
+use solana_sdk_bpf_utils::entrypoint;
 use solana_sdk_bpf_utils::entrypoint::*;
-use solana_sdk_bpf_utils::{entrypoint, info};
 
 entrypoint!(process_instruction);
 fn process_instruction(ka: &mut [SolKeyedAccount], _info: &SolClusterInfo, _data: &[u8]) -> bool {
@@ -18,6 +11,5 @@ fn process_instruction(ka: &mut [SolKeyedAccount], _info: &SolClusterInfo, _data
     // is seen by the runtime and fails as expected
     *ka[0].lamports -= 1;
 
-    info!("Success");
     true
 }