Rollup merge of #22402 - nagisa:spring-cleanup-2, r=nikomatsakis

This commit mostly replaces some of the uses of os::args with env::args.

This, for obvious reasons is based on top of #22400. Do not r+ before that lands.

diff --cc src/rustbook/main.rs
index a8466465f871bdce7c2c0cc15e208a0aa4460ac2,9cfcb0ba227a1a703b243d7a5777e5b45f30650f..cfd4379497a05e4de91f29cfc1a206b4abf307ee
--- 1/src/rustbook/main.rs
--- 2/src/rustbook/main.rs
+++ b/src/rustbook/main.rs
@@@ -48,9 -49,9 +49,9 @@@ mod javascript
  #[cfg(not(test))] // thanks #12327
  fn main() {
      let mut term = Term::new();
-     let cmd = os::args();
+     let cmd: Vec<_> = env::args().collect();
  
 -    if cmd.len() < 1 {
 +    if cmd.len() <= 1 {
          help::usage()
      } else {
          match subcommand::parse_name(&cmd[1][]) {