Revive cache cleaning

The idea here is that, on CI, we only want to cache crates.io
dependencies, and not local crates. This keeps the size of the cache
low, and also improves performance, as network and moving files on
disk (on Windows) can be slow.

xtask/src/main.rs

@@ -17,9 +17,10 @@ use xtask::{
     install::{ClientOpt, InstallCmd, Malloc, ServerOpt},
     metrics::MetricsCmd,
     not_bash::pushd,
+    pre_cache::PreCacheCmd,
     pre_commit, project_root,
     release::{PromoteCmd, ReleaseCmd},
-    run_clippy, run_fuzzer, run_pre_cache, run_rustfmt, Result,
+    run_clippy, run_fuzzer, run_rustfmt, Result,
 };
 
 fn main() -> Result<()> {
@@ -100,7 +101,7 @@ FLAGS:
         }
         "pre-cache" => {
             args.finish()?;
-            run_pre_cache()
+            PreCacheCmd.run()
         }
         "release" => {
             let dry_run = args.contains("--dry-run");