Reformat imports to a consistent style for imports

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

runtime/src/execute_cost_table.rs

@@ -4,8 +4,7 @@
 /// When its capacity limit is reached, it prunes old and less-used programs
 /// to make room for new ones.
 use log::*;
-use solana_sdk::pubkey::Pubkey;
-use std::collections::HashMap;
+use {solana_sdk::pubkey::Pubkey, std::collections::HashMap};
 
 // prune is rather expensive op, free up bulk space in each operation
 // would be more efficient. PRUNE_RATIO defines the after prune table