Update clippy settings and fix a few clippy warnings.

lib/codegen/src/dce.rs

@@ -9,7 +9,6 @@ use crate::entity::EntityRef;
 use crate::ir::instructions::InstructionData;
 use crate::ir::{DataFlowGraph, Function, Inst, Opcode};
 use crate::timing;
-use std::vec::Vec;
 
 /// Test whether the given opcode is unsafe to even consider for DCE.
 fn trivially_unsafe_for_dce(opcode: Opcode) -> bool {
@@ -46,9 +45,7 @@ pub fn do_dce(func: &mut Function, domtree: &mut DominatorTree) {
     let _tt = timing::dce();
     debug_assert!(domtree.is_valid());
 
-    let mut live = Vec::with_capacity(func.dfg.num_values());
-    live.resize(func.dfg.num_values(), false);
-
+    let mut live = vec![false; func.dfg.num_values()];
     for &ebb in domtree.cfg_postorder() {
         let mut pos = FuncCursor::new(func).at_bottom(ebb);
         while let Some(inst) = pos.prev_inst() {