Reformat imports to a consistent style for imports

rustfmt.toml configuration:
  imports_granularity = "One"
  group_imports = "One"

sdk/benches/short_vec.rs

@@ -1,9 +1,7 @@
 #![feature(test)]
 
 extern crate test;
-use bincode::deserialize;
-use solana_sdk::short_vec::ShortVec;
-use test::Bencher;
+use {bincode::deserialize, solana_sdk::short_vec::ShortVec, test::Bencher};
 
 // Return a ShortVec with 127 bytes
 fn create_encoded_short_vec() -> Vec<u8> {